Who's Looking Through The Black Gate?

I've read theories that the weirwood face on the Black Gate is Bran's and the drop of salty water is a tear shed at seeing himself and his companions and what may or may not happen to them north of the Wall.
I like the idea that If future Bran is in control of the gate he still has to let them through because Sam says the words.  If he can control who goes through despite the words being said, he has to let them through despite knowing whats going to happen.


The tear itself is interesting because it's salt water. The other weirwood face that looks as if it had been crying, had tears of the tree's red sap. 

The face carved into the bone pale trunk was long and sad; red tears of dried sap leaked from its eyes. Was that how it looked when we came north? Sam couldn't recall. A Storm of Swords - Samwell III

The droplet of water being salty could be seawater, although the ice the Wall is made from is said to come from lakes in the Haunted Forest

Once, it was said, they had quarried immense blocks of ice from frozen lakes deep in the haunted forest, dragging them south on sledges so the Wall might be raised ever higher. A Game of Thrones - Jon V

What the Wall is made of and what keeps it frozen is another discussion entirely. So sticking to the Gate.....

The Black Gate is obviously different. 
Its glows

....A glow, came from the wood, like milk and moonlight, so faint it scarcely seemed to touch anything beyond the door itself, not even Sam standing right before it. A Storm of Swords Bran IV

it talks,

...."Who are you?" the door asked, and the well whispered, "Who-who-who-who-who-who-who." A Storm of Swords Bran IV

and of course it can open its mouth....very wide

...."Then pass," the door said. Its lips opened, wide and wider and wider still, until nothing at all remained but a great gaping mouth in a ring of wrinkles....A Storm of Swords Bran IV

Bran describes the face on the Gate as...

 The face was old and pale, wrinkled and shrunken. It looks dead. Its mouth was closed, and its eyes; its cheeks were sunken, its brow withered, its chin sagging. If a man could live for a thousand years and never die but just grow older, his face might come to look like that. A Storm of Swords - Bran IV

If a weirwood face takes on the likeness of the person looking through it, is it the same for the gate?  

And is there anyone who looks like this in the story?

The description of the face could be Future Bran...maybe. We obviously dont know what he will look like when he is an old man or if he will be alive at the age the face seems to be. If he is still in Bloodraven's cave, resting in the roots of a weirwood i think he would resemble what Bloodraven looks like now with roots growing through his body. 
If Bloodraven controls the Black Gate, i think it would have a much scarier face than the old man's face Bran describes.

The face Bran describes is more like Maester Aemon...

"Aye."

"Aemon Targaryen?"

"Once. Most just called him Maester Aemon. He died during our voyage south. How is it that you know of him?"

"How not? He was more than just the oldest living maester. He was the oldest man in Westeros, and lived through more history than Archmaester Perestan has ever learned. He could have told us much and more about his father's reign, and his uncle's. How old was he, do you know?"

"One hundred and two." A Feast for Crows Samwell V

"Nonetheless," Maester Aemon said as his clouded, milk-white eyes moved to Tyrion's face, "I think it is true."
For once, Tyrion Lannister found himself at a loss for words. He could only bow his head politely and say, "You are too kind, Maester Aemon."
The blind man smiled. He was a tiny thing, wrinkled and hairless, shrunken beneath the weight of a hundred years so his maester's collar with its links of many metals hung loose about his throat. "I have been called many things, my lord," he said, "but kind is seldom one of them." This time Tyrion himself led the laughter. Tyrion III AGOT

Maester Aemon had counted more than a hundred name days, Jon knew. Frail, shrunken, wizened, and blind, it was hard to imagine him as a little boy no older than Arya. A Clash of Kings - Jon I

The face on the gate is blind,

.....The door opened its eyes.

They were white too, and blind. "Who are you?" the door asked, and the well whispered, "Who-who-who-who-who-who-who."ASOS-Bran IV

So is there any evidence for Aemon being able to do this ?

Bran's third eye powers go up a level from wolfdreams to warging when he is hiding in the darkness of the crypts.

He remembered who he was all too well; Bran the boy, Bran the broken. Better Bran the beastling. Was it any wonder he would sooner dream his Summer dreams, his wolf dreams? Here in the chill damp darkness of the tomb his third eye had finally opened. He could reach Summer whenever he wanted, and once he had even touched Ghost and talked to Jon. A Clash of Kings - Bran VII

Arya's powers go up when her eye's are taken by the House of Black and White

I saw you. "I gave you three. I don't need to give you four." Maybe on the morrow she would tell him about the cat that had followed her home last night from Pynto's, the cat that was hiding in the rafters, looking down on them. Or maybe not. If he could have secrets, so could she. A Dance with Dragons - The Blind Girl

Bloodraven tells Bran,

"Never fear the darkness, Bran." The lord's words were accompanied by a faint rustling of wood and leaf, a slight twisting of his head. "The strongest trees are rooted in the dark places of the earth. Darkness will be your cloak, your shield, your mother's milk. Darkness will make you strong." A Dance with Dragons- Bran III

Aemon's Blindness may have awoken power's he already had. The Stark's have Wolf dreams,Targaryen's have Dragon dreams. If Aemon's "power" did awaken when he lost his sight,it's more than likely that it would be raven's eye's he would see through.

Aemon does mention spending his night's with Ghost's

"I am sorry to have woken you, Maester," Jon Snow said.

"You did not wake me," Maester Aemon replied. "I find I need less sleep as I grow older, and I am grown very old. I often spend half the night with ghosts, remembering times fifty years past as if they were yesterday. The mystery of a midnight visitor is a welcome diversion. So tell me, Jon Snow, why have you come calling at this strange hour?" A Game of Thrones - Jon V

Despite being blind he is able to  work on Jon's wound's when he comes back from his time with the Free Folk

A fire was burning in the hearth, and the room was almost stuffy. The warmth made Jon sleepy. As soon as Noye eased him down onto his back, he closed his eyes to stop the world from spinning. He could hear the ravens quorking and complaining in the rookery above."Snow," one bird was saying. "Snow, snow, snow." That was Sam's doing, Jon remembered. Had Samwell Tarly made it home safely, he wondered, or only the birds?

Maester Aemon was not long in coming. He moved slowly, one spotted hand on Clydas's arm as he shuffled forward with small careful steps. Around his thin neck his chain hung heavy, gold and silver links glinting amongst iron, lead, tin, and other base metals. "Jon Snow," he said, "you must tell me all you've seen and done when you are stronger. Donal, put a kettle of wine on the fire, and my irons as well. I will want them red-hot. Clydas, I shall need that good sharp knife of yours." The maester was more than a hundred years old; shrunken, frail, hairless, and quite blind. But if his milky eyes saw nothing, his wits were still as sharp as they had ever been. A Storm of Swords- Jon VI

There have been a few times that Maester Aemon seems to see things despite being blind

"I … ah … Maester Aemon wants to see you."

It was not time for his bandages to be changed. Jon frowned suspiciously. "Why?" he demanded. Sam looked miserable. That was answer enough. "You told him, didn't you?" Jon said angrily. "You told him that you told me."

"I … he … Jon, I didn't want to … he asked … I mean … I think he knew, he sees things no one else sees …"

"He's blind," Jon pointed out forcefully, disgusted. "I can find the way myself." He left Sam standing there, openmouthed and quivering. A Game of Thrones - Jon VIII

Jon goes to see Maester Aemon in the rookery. His Ravens seem very hungry...

Jon shifted the bucket to his right hand and thrust his left down into the bloody bits. The ravens began to scream noisily and fly at the bars, beating at the metal with night-black wings. The meat had been chopped into pieces no larger than a finger joint. He filled his fist and tossed the raw red morsels into the cage, and the squawking and squabbling grew hotter. Feathers flew as two of the larger birds fought over a choice piece. Quickly Jon grabbed a second handful and threw it in after the first. "Lord Mormont's raven likes fruit and corn."
"He is a rare bird," the maester said. "Most ravens will eat grain, but they prefer flesh. It makes them strong, and I fear they relish the taste of blood. In that they are like men … and like men, not all ravens are alike."A Game of Thrones - Jon VIII

...but when Aemon tells Jon he must choose,some seem to stop eating and have a look at Jon, or is it Aemon that's having a look?

..."A craven can be as brave as any man, when there is nothing to fear. And we all do our duty, when there is no cost to it. How easy it seems then, to walk the path of honor. Yet soon or late in every man's life comes a day when it is not easy, a day when he must choose."
Some of the ravens were still eating, long stringy bits of meat dangling from their beaks. The rest seemed to be watching him. Jon could feel the weight of all those tiny black eyes. "And this is my day … is that what you're saying?"
Maester Aemon turned his head and looked at him with those dead white eyes. It was as if he were seeing right into his heart. Jon felt naked and exposed. He took the bucket in both hands and flung the rest of the slops through the bars. Strings of meat and blood flew everywhere, scattering the ravens. They took to the air, shrieking wildly. The quicker birds snatched morsels on the wing and gulped them down greedily. Jon let the empty bucket clang to the floor.A Game of Thrones - Jon VIII

After Maester Aemon sent two letters to King's Landing, both of which are ignored...



 "Perhaps they never got my letter. Aemon sent two copies, with his best birds, but who can say? More like, Pycelle did not deign to reply. It would not be the first time, nor the last. I fear we count for less than nothing in King's Landing. They tell us what they want us to know, and that's little enough."  A Game of Thrones Jon VIII



...Mormont sends ser Alliser Thorne to King's Landing with the wight's hand... 



Mormont snorted. "Because I sent him, why do you think? He's bringing the hand your Ghost tore off the end of Jafer Flowers's wrist. I have commanded him to take ship to King's Landing and lay it before this boy king. That should get young Joffrey's attention, I'd think … and Ser Alliser's a knight, highborn, anointed, with old friends at court, altogether harder to ignore than a glorified crow."


"Crow." Jon thought the raven sounded faintly indignant.   A Game of Thrones Jon VIII

Mormont's raven seems to take offence when the Lord Commander refers to Maester Aemon as a 'glorified crow'.

When the Night's Watch make cap on the Fist of the First Men Mormont asks Jon a question,

Mormont dug into a sack and offered his raven a handful of
corn. “You think I’m wrong to keep the rangers close?”
“That’s not for me to say, my lord.”
“It is if you’re asked.”
“If the rangers must stay in sight of the Fist, I don’t see how they can hope to find my uncle,”
Jon admitted.
“They can’t.” The raven pecked at the kernels in the Old Bear ’s palm. “Two hundred men or
ten thousand, the country is too vast.” The corn gone, Mormont turned his hand over.
“You would not give up the search?”
“Maester Aemon thinks you clever.” Mormont moved the raven to his shoulder. The bird tilted
its head to one side, little eyes a-glitter.
The answer was there. “Is it… it seems to me that it might be easier for one man to find two
hundred than for two hundred to find one.”
The raven gave a cackling scream, but the Old Bear smiled through the grey of his beard.
“This many men and horses leave a trail even Aemon could follow. On this hill, our fires ought to
be visible as far off as the foothills of the Frostfangs. If Ben Stark is alive and free, he will come to
us, I have no doubt.”
“Yes,” said Jon, “but… what if…”
“…he’s dead?” Mormont asked, not unkindly.
Jon nodded, reluctantly.
“Dead,” the raven said. “Dead. Dead.”
“He may come to us anyway,” the Old Bear said. “As Othor did, and Jafer Flowers. I dread that
as much as you, Jon, but we must admit the possibility.”
“Dead,” his raven cawed, ruffling its wings. Its voice grew louder and more shrill. “Dead.” A Clash of Kings Jon IV



Could Maester Aemon be skinchanging  Mormont's raven and the others to see whats going on at Castle Black? Is this how  "....he sees things no one else sees …" ?


If Aemon has the ability to see through the eyes of the ravens at Castle Black, could he be controlling the Black Gate?   
Maybe.  
The description of Aemon  and the Black Gate in these two passages are similar-

What could I have done, old, blind, frail? I was helpless as a suckling babe, yet still it grieved me to sit forgotten as they cut down my brother's poor grandson, and his son, and even the little children …"

Jon was shocked to see the shine of tears in the old man's eyes. "Who are you?" he asked quietly, almost in dread.
A toothless smile quivered on the ancient lips. "Only a maester of the Citadel, bound in service to Castle Black and the Night's Watch. In my order, we put aside our house names when we take our vows and don the collar."   A Game of Thrones Jon VIII

....The door opened its eyes.

They were white too, and blind. "Who are you?" the door asked, and the well whispered, "Who-who-who-who-who-who-who."

"I am the sword in the darkness," Samwell Tarly said. "I am the watcher on the walls. I am the fire that burns against the cold, the light that brings the dawn, the horn that wakes the sleepers. I am the shield that guards the realms of men."

"Then pass," the door said. Its lips opened, wide and wider and wider still, until nothing at all remained but a great gaping mouth in a ring of wrinkles. Sam stepped aside and waved Jojen through ahead of him. Summer followed, sniffing as he went, and then it was Bran's turn. Hodor ducked, but not low enough. The door's upper lip brushed softly against the top of Bran's head, and a drop of water fell on him and ran slowly down his nose. It was strangely warm, and salty as a tear.  A Storm of Swords - Bran IV

When the door asks "who are you and the well whispered,"Who-who-who-who-who-who-who." it reminded me of Mormont's Raven 

"The Long Night has come before. Oh, eight thousand years is a good while, to be sure … yet if the Night's Watch does not remember, who will?"
"Who will," chimed the talkative raven. "Who will."   A Game of Thrones Jon VIII

The description of the gate and how it works is still unclear because we only see one side of it.


Sam and Gilly come through the Black Gate from the north side to the south side and arrive under the Nightfort.

"How did you get through the Wall?" Jojen demanded as Sam struggled to his feet. "Does the well lead to an underground river, is that where you came from? You're not even wet . . ." "There's a gate," said fat Sam. "A hidden gate, as old as the Wall itself. The Black Gate, he called it."ASOS Bran IV

Then Sam leads Bran and co down the well to the gate,

The Black Gate, Sam had called it, but it wasn't black at all. It was white weirwood, and there was a face on it.

Its mouth was closed, and its eyes; its cheeks were sunken, its brow withered, its chin sagging. If a man could live for a thousand years and never die but just grow older, his face might come to look like that. ASOS Bran IV

Did the gate look and work the same way when Sam came to it from the north side? 
Did Sam say the words (on the north side) and the weirwood face opened its mouth for him and Gilly to walk through? If so does this mean there is a face carved on both sides of the gate or does it open on one side then close behind to open again on the other side?

This whole process reminded me of the three headed god Trios.

"One time, the girl remembered, the Sailor's Wife had walked her rounds with her and told her tales of the city's stranger gods. "That is the house of the Great Shepherd. Three-headed Trios has that tower with three turrets. The first head devours the dying, and the reborn emerge from the third. I don't know what the middle head's supposed to do."
A Dance With Dragons- The Ugly Little Girl

When someone goes through the Gate, it must look like it's devouring them like Trios devours the dead only to emerge on the other side reborn. And just like the Sailor's Wife, we don't know what happens on the journey inbetween.

"Allow me to give my lord one last piece of counsel," the old man had said, "the same counsel that I once gave my brother when we parted for the last time. He was three-and-thirty when the Great Council chose him to mount the Iron Throne. A man grown with sons of his own, yet in some ways still a boy. Egg had an innocence to him, a sweetness we all loved. Kill the boy within you, I told him the day I took ship for the Wall. It takes a man to rule. An Aegon, not an Egg. Kill the boy and let the man be born." The old man felt Jon's face. "You are half the age that Egg was, and your own burden is a crueler one, I fear. You will have little joy of your command, but I think you have the strength in you to do the things that must be done. Kill the boy, Jon Snow. Winter is almost upon us. Kill the boy and let the man be born." A Dance with Dragons - Jon II

Male And Female In The Vale Of Arryn

Swords Of Ice And Fire

The Trident Has Three Heads

Aerys,Tywin And A Bride For Rhaegar

Davos's Thumb

Coin Well Spent

Valonqar - High Valyrian Or Bastard Valyrian?

Brandon's Bastards

Male And Female In The Vale Of Arryn

Reading the chapter  AGOT Catelyn VI,  Catelyn's Journey to the Eyrie and her description of the area and the different structures, gates and landmarks, I noticed that the Vale of Arryn can be seen to look like both male and female reproductive systems. 

Catelyn's journey up the Mountain Road through the Mountains of the Moon, leads her to the Bloody Gate. A defensive structure that guards the Vale of Arryn. Before the gate we see in the story was constructed, the road to the Vale was protected by a wall,

....Its eastern end is guarded by the Bloody Gate, once merely a rough-hewn, unmortared wall after the fashion of the ringforts of the First Men. But in the reign of King Osric V Arryn, this fortress was constructed a new. Over the centuries, a dozen invading armies have smashed themselves to pieces attempting to breach the Bloody Gates.  The World of Ice and Fire- The Vale

 

The original rough-hewn wall that guarded the Vale may have been similar to the ring forts built by the First Men but i dont believe it would be the same  ring shape, although i do believe it could have curved between the rocky slopes. 

The original gate is no longer there but this unmortared style of construction is seen again on the Giants Lance at  the second and third waycastles, Snow and Sky.

An unmortared stone wall at Snow...

....Snow was smaller than Stone, a single fortified tower and a timber keep and stable hidden behind a low wall of unmortared rock. Yet it nestled against the Giant's Lance in such a way as to command the entire stone stair above the lower waycastle....A Game of Thrones - Catelyn VI

The unmortared, stone wall of Sky...

...The waycastle called Sky was no more than a high, crescent-shaped wall of unmortared stone raised against the side of the mountain, but even the topless towers of Valyria could not have looked more beautiful to Catelyn Stark....  A Game of Thrones- Catelyn VI  

 Whether the wall was curved or straight, the original gate was the first barrier to the Vale. This "gate" would most likely have been maintained as a defense while the construction of  the Bloody Gate was carried out behind it before it was removed. 

The curved, crescent shape is seen throughout the Vale and the Eyrie. 

On the weirwood Moon Door,

...When she saw the crescent moon carved in the wood, she planted her feet. "The Moon Door." She tried to yank free. "Why are you showing me the Moon Door?"    A Storm of Swords, Sansa VII

and the brooch worn by Sweetrobin,

  ...Robert did not need to know that, though. He was only a sick little boy who'd loved his mother. "There," Sansa said, "you look a proper lord now. Maddy, fetch his cloak." It was lambswool, soft and warm, a handsome sky-blue that set off the cream color of his tunic. She fastened it about his shoulders with a silver brooch in the shape of a crescent moon, and took him by the hand. Robert came meekly for once.   A Feast for Crows  Sansa I

and also worn by some Vale knights like sir Hugh of the Vale,

 ..."He must have cut a gallant figure in the tourney, him in his bright new armor, with those crescent moons on his cloak. A pity he died so untimely, before you could talk to him …"Ned felt half-poisoned himself. "The squire," he said. "Ser Hugh." Wheels within wheels within wheels. Ned's head was pounding. "Why? Why now? Jon Arryn had been Hand for fourteen years. What was he doing that they had to kill him?"   A Game of Thrones - Eddard VII

Alayne Stone meets the Lords Declarant  in the Crescent Chamber,

..."The Lord Protector awaits you in the solar. If my lords would follow me." From the Crescent Chamber they climbed a steep flight of marble steps that bypassed both undercrofts and dungeons and passed beneath three murder holes, which the Lords Declarant pretended not to notice.  A Feast for Crows  Alayne I.

The arms of House Egan,

According to the Ice and fire wiki, the Arms of house Arryn are A sky-blue falcon soaring against a white moon, on a sky-blue field. 

 The sigil in the books is described as "moon and falcon", and the World of Ice and fire show them as a falcon on a full moon but the crescent moon shape seems to be found throughout the Eyrie. It is a shape associated with House Arryn and the Vale. The crescent shape can be associated with virginity,

The crescent moon is a major attribute of the virgin goddess Diana and her Greek equivalent Artemis. They are often depicted wearing a crescent moon on their heads.
.                                                                      The crescent moon represents the Maiden and the Crone in the Triple Goddess symbol,


The Virgin Mary is often depicted with a crescent moon.

.....hymenal openings come in many shapes, depending on hormonal and activity level, the most common being crescentic (posterior rim): no tissue at the 12 o'clock position; crescent-shaped band of tissue from 1–2 to 10–11 o'clock, at its widest around 6 o'clock.  https://en.wikipedia.org/wiki/Hymen

 

similar to the sigil used on the show

side note- A crescent moon on the night  Bran is "wed" to the trees. Brans "wedding night"

 ...The moon was a crescent, thin and sharp as the blade of a knife. The days marched
past, one after the other, each shorter than the one before. The nights grew longer. No
sunlight ever reached the caves beneath the hill. No moonlight ever touched those stony
halls. Even the stars were strangers there. Those things belonged to the world above,
where time ran in its iron circles, day to night to day to night to day.
“It is time,” Lord Brynden said.
Something in his voice sent icy fingers running up Bran’s back. “Time for what?”
“For the next step. For you to go beyond skinchanging and learn what it means to be a
greenseer.”   A Dance with Dragons - Bran III

The structure that guards the Vale now, the Bloody Gate, is described as two watchtowers joined by a covered bridge over the road.  

.....Catelyn had more faith in a maester's learning than a septon's prayers. She was about to say as much when she saw the battlements ahead, long parapets built into the very stone of the mountains on either side of them. Where the pass shrank to a narrow defile scarce wide enough for four men to ride abreast, twin watchtowers clung to the rocky slopes, joined by a covered bridge of weathered grey stone that arched above the road.  A Game of Thrones- Catelyn VI

To me this is describing the female reproductive system, the two towers connected over the road symbolizing the ovaries.

                                                            original gate

The removal of the original gate is a "deflowering". The gate being rebuilt to a gate that "a dozen armies had dashed themselves to pieces in the Age of Heroes." leading to it's name,The Bloody Gate, is symbolic of a girl who has flowered to maidenhood. 

....And so she rode behind him, beneath the shadow of the Bloody Gate where a dozen armies had dashed themselves to pieces in the Age of Heroes. On the far side of the stoneworks, the mountains opened up suddenly upon a vista of green fields, blue sky, and snow capped mountains that took her breath away. The Vale of Arryn bathed in the morning light.

It stretched before them to the misty east, a tranquil land of rich black soil, wide slow-moving rivers, and hundreds of small lakes that shone like mirrors in the sun, protected on all sides by its sheltering peaks. Wheat and corn and barley grew high in its fields, and even in Highgarden the pumpkins were no larger nor the fruit any sweeter than here. They stood at the western end of the valley, where the high road crested the last pass and began its winding descent to the bottomlands two miles below. The Vale was narrow here, no more than a half day's ride across, and the northern mountains seemed so close that Catelyn could almost reach out and touch them. A Game of Thrones- Catelyn VI

Beyond that, is the Vale itself. This symbolizes the womb. The western end of the Vale at the Bloody Gate is narrow and widens out to the east.

This "womb" is some of the most fertile land in Westeros. 

.....It stretched before them to the misty east, a tranquil land of rich black soil, wide slow-moving rivers, and hundreds of small lakes that shone like mirrors in the sun, protected on all sides by its sheltering peaks. Wheat and corn and barley grew high in its fields, and even in Highgarden the pumpkins were no larger nor the fruit any sweeter than here. A Game of Thrones- Catelyn VI




At the Gates of the Moon there is a moat. This is where the landmarks switch to male symbology 

....Even so, it was full dark before they reached the stout castle that stood at the foot of the Giant's Lance. Torches flickered atop its ramparts, and the horned moon danced upon the dark waters of its moat. The drawbridge was up and the portcullis down, but Catelyn saw lights burning in the gatehouse and spilling from the windows of the square towers beyond.

"The Gates of the Moon," her uncle said as the party drew rein. His standard-bearer rode to the edge of the moat to hail the men in the gatehouse. "Lord Nestor's seat. He should be expecting us. Look up." A Game of Thrones- Catelyn VI

                               

Over the moat, the Gates of the Moon is described as a 'stout castle that stood at the foot of the Giants Lance'. I think GRRM is having a bit of fun here and is describing a fat butt. To 'moon' or 'mooning' is to expose the buttocks in order to offend. The Gates of the Moon are the  'Gates of the Ass'.  "Lord Nestor's seat..."

Definition of seat

noun

something designed to support a person in a sitting position, as a chair, bench, or pew; a place on or in which one sits.

the part of a chair, sofa, or the like, on which one sits.

the part of the body on which one sits; the buttocks.

dictionary.com

 Further on at the base of the mountain the first waycastle is called Stone. The path to stone is covered by forest. Stone is surrounded by a stone wall topped with iron spikes and has two fat round towers. I think Stone should be called 'Stones'.

....The trees pressed close, leaning over the path to make a rustling green roof that shut out even the moon, so it seemed as though they were moving up a long black tunnel. But the mules were surefooted and tireless, and Mya Stone did indeed seem blessed with night-eyes. They plodded upward, winding their way back and forth across the face of the mountain as the steps twisted and turned. A thick layer of fallen needles carpeted the path, so the shoes of their mules made only the softest sound on the rock. The quiet soothed her, and the gentle rocking motion set Catelyn to swaying in her saddle. Before long she was fighting sleep. 
Perhaps she did doze for a moment, for suddenly a massive ironbound gate was looming before them. "Stone," Mya announced cheerily, dismounting. Iron spikes were set along the tops of formidable stone walls, and two fat round towers overtopped the keep. A Game of Thrones- Catelyn VI 

 

The mountain itself is called the Giants Lance which i dont think needs explaining but there are some things that stand out (pardon the pun).

Directly above Stone, is the second waycastle, Snow. Snow is an unmortared stone structure built against the Giant's Lance...

...Snow was smaller than Stone, a single fortified tower and a timber keep and stable hidden behind a low wall of unmortared rock. Yet it nestled against the Giant's Lance in such a way as to command the entire stone stair above the lower waycastle. An enemy intent on the Eyrie would have to fight his way from Stone step by step, while rocks and arrows rained down from Snow above. A Game of Thrones - Catelyn VI


The third waycastle, Sky, is also the same type of construction as the original gate to the Vale.

...Tyrion's arms were too short to reach the plate, and he was not about to step that close to the edge. All it would take would be a quick shove of Mord's heavy white belly, and he would end up a sickening red splotch on the stones of Sky, like so many other prisoners of the Eyrie over the centuries.  A Game of Thrones - Tyrion V


The stones of Sky have been stained with blood over the years.... 



 ...Brandon was never shy about taking what he wanted. I am old now, a dried-up thing, too long a widow, but I still remember the look of my maiden's blood on his cock the night he claimed me. I think Brandon liked the sight as well. A bloody sword is a beautiful thing, yes. It hurt, but it was a sweet pain...A Dance with Dragons - The Turncloak


The  stones that were used to build the unmortared stone walls of Snow and Sky may be remnants of the original gate that guarded the Vale staining the mountain like maidens blood.


'A bloody sword is a beautiful thing,' he told me once."....A Dance with Dragons - The Turncloak

Catelyn sees beauty in them...

...The waycastle called Sky was no more than a high, crescent-shaped wall of unmortared stone raised against the side of the mountain, but even the topless towers of Valyria could not have looked more beautiful to Catelyn Stark.... A Game of Thrones - Catelyn VI


At the top of the Giants Lance is the start of a waterfall called Alyssa's Tears. The waters of Alyssa's Tears, falls from such a height, that it turns to mist, never reaching the Vale.

....Looming over them all was the jagged peak called the Giant's Lance, a mountain that even mountains looked up to, its head lost in icy mists three and a half miles above the valley floor. Over its massive western shoulder flowed the ghost torrent of Alyssa's Tears. Even from this distance, Catelyn could make out the shining silver thread, bright against the dark stone. A Game of Thrones- Catelyn VI

Alyssa's Tears is named for Alyssa Arryn who saw her whole family murdered in front of her and never shed a tear. After her own death, the gods cursed her that she would not know rest until her tears reached the Vale of Arryn, where all those she had loved were buried.

....Pale white mists rose off Alyssa's Tears, where the ghost waters plunged over the shoulder of the mountain to begin their long tumble down the face of the Giant's Lance. Catelyn could feel the faint touch of spray on her face.
Alyssa Arryn had seen her husband, her brothers, and all her children slain, and yet in life she had never shed a tear. So in death, the gods had decreed that she would know no rest until her weeping watered the black earth of the Vale, where the men she had loved were buried. Alyssa had been dead six thousand years now, and still no drop of the torrent had ever reached the valley floor far below. Catelyn wondered how large a waterfall her own tears would make when she died. "Tell me the rest of it," she said.A Game of Thrones- Catelyn VII

The Eyrie itself has some interesting features..

The walls of the High Hall of the Arryn's in the Eyrie are blue veined marble,

....That would have been a very good time to have kept his mouth closed and his head bowed. He could see that now; seven hells, he had seen it then. The High Hall of the Arryns was long and austere, with a forbidding coldness to its walls of blue-veined white marble, but the faces around him had been colder by far. The power of Casterly Rock was far away, and there were no friends of the Lannisters in the Vale of Arryn. Submission and silence would have been his best defenses.   A Game of Thrones - Tyrion V

with a blue silk carpet running the through the length of the hall,

....Sansa walked down the blue silk carpet between rows of fluted pillars slim as lances. The floors and walls of the High Hall were made of milk-white marble veined with blue. Shafts of pale daylight slanted down through narrow arched windows along the eastern wall. Between the windows were torches, mounted in high iron sconces, but none of them was lit. Her footsteps fell softly on the carpet. Outside the wind blew cold and lonely.  A Storm of Swords - Sansa VII



It seems that GRRM has built the Vale and its landmarks to symbolize a fertile woman and an infertile man.

The original gate no longer being there symbolizes the maidenhead has been taken.

The Bloody Gate built behind it symbolizes the female has flowered and is of childbearing age.

The fertile land of the Vale symbolizes the fertility of her womb and the ability to have children.

The stones from the original gate possibly being used to build the waycastles Snow and Sky show the male has performed the act.(maidens blood on the 'bloody sword')

The Waterfall(seed) never touches the Vale below symbolizes  he has not impregnated the woman.

Except for the virginity, this is analogous of the marriage of Jon Arryn to Lysa Tully.

Lysa, the fertile woman,

... An old man without an heir. His first two wives had left him childless, his brother's son had been murdered with Brandon Stark in King's Landing, his gallant cousin had died in the Battle of the Bells. He needed a young wife if House Arryn was to continue . . . a young wife known to be fertile.
 A Storm of Swords - Catelyn I

Jon Arryn, the husband,


 .... That was hard, to see him every day and still be wed to that old cold man. Jon did his duty in the bedchamber, but he could no more give me pleasure than he could give me children. His seed was old and weak. All my babies died but Robert, three girls and two boys. All my sweet little babies dead, and that old man just went on and on with his stinking breath......  A Storm of Swords - Sansa VI

There have obviously been children born to House Arryn that lived to have children of their own. There isn't a lot of info on House Arryn but the other members who lived away from the Eyrie seem to have no problems conceiving children, and had quite big families. 
Robert Arryn (Sweetrobin) was born outside of the Vale,

...Robert had never learned to ride properly, she knew. Mules, horses, donkeys, it made no matter; to him they were all fearsome beasts, as terrifying as dragons or griffins. He had been brought to the Vale at six, riding with his head cradled between his mother's milky breasts, and had never left the Eyrie since.  A Feast for Crows - Alayne II

I believe Alyssa's curse is the reason that House Arryn is plagued by stillbirths miscarriages, infant deaths and mothers dying in the birthing bed.  Alyssa never shedding a tear at the deaths of her family could mean she may have had something to do with the deaths and may be cursed as a Kinslayer.
The waterfall of the Giants Lance(male) never fertilizes the apparently fertile Vale(female) below.


Not much grows at the Eyrie...

...Lysa's apartments opened over a small garden, a circle of dirt and grass planted with blue flowers and ringed on all sides by tall white towers. The builders had intended it as a godswood, but the Eyrie rested on the hard stone of the mountain, and no matter how much soil was hauled up from the Vale, they could not get a weirwood to take root here. So the Lords of the Eyrie planted grass and scattered statuary amidst low, flowering shrubs. It was there the two champions would meet to place their lives, and that of Tyrion Lannister, into the hands of the gods. A Game of Thrones - Catelyn VII

The word "impregnable" comes up when speaking about the castle.

...The eastern road was wilder and more dangerous, climbing through rocky foothills and thick forests into the Mountains of the Moon, past high passes and deep chasms to the Vale of Arryn and the stony Fingers beyond. Above the Vale, the Eyrie stood high and impregnable, its towers reaching for the sky.  A Game of Thrones - Catelyn V



,,,Lysa covered her boy's ear with her hand. "Even if they could bring an army through the mountains and past the Bloody Gate, the Eyrie is impregnable. You saw for yourself. No enemy could ever reach us up here."  A Game of Thrones - Catelyn VI

But when Sweetrobin speaks of it in both Alayne chapters in A Feast for Crows, its different...



...."I won't have him here. You send him back down. I never said that he could come. Not here.The Eyrie is impregnable, Mother said." A Feast for Crows- Alayne I

.
..His mouth quivered. "I hate those smelly mules. One tried to bite me once! You tell that Mya that I'm staying here." He sounded as if he were about to cry. "No one can hurt me so long as I stay here. The Eyrie is impregnable."  A Feast for Crows - Alayne II

In the paperback I have,the 'preg' part of the word is italicized for some reason. I cant find it printed this way in any other chapter.
The word "impregnable" is an auto-antonym like Flammable and Inflammable.

An auto-antonym or autantonym, also called a contronym or contranym, is a word with multiple meanings (senses) of which one is the reverse of another. For example, the word cleave can mean "to cut apart" or "to bind together". This phenomenon is called enantiosemy, enantionymy or antilogy (enantio- means "opposite")..... https://en.wikipedia.org/wiki/Auto-antonym

......"Impregnable" can mean "invulnerable" when speaking of a castle and can also mean "vulnerable" to impregnation (pregnant).

. 

Is GRRM playing with the meaning of this word? When he says the Eyrie is impregnable, does he mean Invulnerable to impregnation?



TRIAL BY COMBAT

Tyrion's trial by combat can be seen as another example of Alyssa's Curse.

When ser Vardis Egan and Bronn meet in the Eyrie's garden, they fight beneath a statue of a weeping woman that Catelyn assumes is supposed to be Alyssa,

A bell tolled loudly below them. High lords and serving girls alike broke off what they were doing and moved to the balustrade. Below, two guardsmen in sky-blue cloaks led forth Tyrion Lannister. The Eyrie's plump septon escorted him to the statue in the center of the garden, a weeping woman carved in veined white marble, no doubt meant to be Alyssa. A Game of Thrones Catelyn VII

Ser Vardis will fight with Jon Arryn's sword. Given to him by Lysa,

Ser Vardis held out a gauntleted hand, and his squire placed a handsome double-edged longsword in his grasp. The blade was engraved with a delicate silver tracery of a mountain sky; its pommel was a falcon's head, its crossguard fashioned into the shape of wings. "I had that sword crafted for Jon in King's Landing," Lysa told her guests proudly as they watched Ser Vardis try a practice cut. "He wore it whenever he sat the Iron Throne in King Robert's place. Isn't it a lovely thing? I thought it only fitting that our champion avenge Jon with his own blade."

The sword is often used to represent the penis and in this story we hear Barbry Dustin refer to Brandon Starks penis as a bloody sword. This sword /penis is John Arryn's



The engraved silver blade was beautiful beyond a doubt, but it seemed to Catelyn that Ser Vardis might have been more comfortable with his own sword. Yet she said nothing; she was weary of futile arguments with her sister.

The sword/penis is engraved with a mountain sky and could be said to look like a sword/penis rising up into the mountain sky. Just like the Giant's Lance. The falcon head pommel and the winged crossguard leave no doubt that this is an Arryn sword/penis.

Blind with arrogance as they were, even the knights and lords of the Vale could see what was happening below them, yet her sister could not. "Enough, Ser Vardis!" Lady Lysa called down. "Finish him now, my baby is growing tired."

Ser Vardis is struggling to defeat Bronn and is injured ,but the Knight makes one last effort to slay Tyrion's champion,

And it must be said of Ser Vardis Egen that he was true to his lady's command, even to the last. One moment he was reeling backward, half-crouched behind his scarred shield; the next he charged. The sudden bull rush caught Bronn off balance. Ser Vardis crashed into him and slammed the lip of his shield into the sellsword's face. Almost, almost, Bronn lost his feet … he staggered back, tripped over a rock, and caught hold of the weeping woman to keep his balance. Throwing aside his shield, Ser Vardis lurched after him, using both hands to raise his sword. His right arm was blood from elbow to fingers now, yet his last desperate blow would have opened Bronn from neck to navel … if the sellsword had stood to receive it.

when Alyssa's Curse strikes,

But Bronn jerked back. Jon Arryn's beautiful engraved silver sword glanced off the marble elbow of the weeping woman and snapped clean a third of the way up the blade. Bronn put his shoulder into the statue's back. The weathered likeness of Alyssa Arryn tottered and fell with a great crash, and Ser Vardis Egen went down beneath her.

Ser Vardis's (Jon Arryn's) sword (penis) glances off the statue of Alyssa Arryn and breaks. When Bronn pushes the statue over it pins ser Vardis to the ground. 

Bronn makes an end to it,

Bronn was on him in a heartbeat, kicking what was left of his shattered rondel aside to expose the weak spot between arm and breastplate. Ser Vardis was lying on his side, pinned beneath the broken torso of the weeping woman. Catelyn heard the knight groan as the sellsword lifted his blade with both hands and drove it down and in with all his weight behind it, under the arm and through the ribs. Ser Vardis Egen shuddered and lay still.


THE MOON DOOR

House Arryn is an Andal house. The Vale was taken from the First Men  when the warring Andal kings Joined together behind Artys Arryn to take the Vale from the First Men king Robar II of House Royce....

...But it was not to be. Robar had won his last victory, for the remaining Andal lords and petty kings had finally come to realize their peril. And now it was the Andals who put aside their differences to make common cause and unite beneath the banners of a single warlord. The man they chose to lead them was neither king nor prince, nor even lord, but a knight named Ser Artys Arryn. A young man, of an age with King Robar, he was esteemed amongst his peers as the finest warrior of his day, a champion with sword and lance and morningstar, and a cunning and resourceful leader of men, beloved by all who fought beside him. Though of pure Andal blood, Ser Artys had been born in the Vale in the shadow of the Giant's Lance, where falcons soared amongst the mountain's jagged peaks. On his shield he bore the moon-and-falcon, whilst a pair of falcon's wings decorated his silver warhelm. The Falcon Knight, men called him, then as now. The World of Ice and Fire - The Vale

The Arryns tried, unsuccessfully, to plant a weirwood in their godswood at the Eyrie.
A weirwood tree would never take root at the Eyrie but the throne of the Arryns is made of weirwood and so is the Moon door.

...The press of spectators parted. A narrow weirwood door stood between two slender marble pillars, a crescent moon carved in the white wood. Those standing closest edged backward as a pair of guardsmen marched through. One man removed the heavy bronze bars; the second pulled the door inward. Their blue cloaks rose snapping from their shoulders, caught in the sudden gust of wind that came howling through the open door. Beyond was the emptiness of the night sky, speckled with cold uncaring stars. 
 "Behold the king's justice," Lysa Arryn said. Torch flames fluttered like pennons along the walls, and here and there the odd torch guttered out.  A Game of Thrones - Tyrion V

The Moon Door is used to dispense the king's justice but Littlefinger uses it to murder Lysa Arryn...

Lysa Arryn smiled tremulously. "Only one? Oh, Petyr, do you swear it? Only one?"

..."Only Cat." He gave her a short, sharp shove. Lysa stumbled backward, her feet slipping on the wet marble. And then she was gone. She never screamed. For the longest time there was no sound but the wind.   A Storm of Swords - Sansa VII

But could it have once been used for something else?  Perhaps a fertility sacrifice to appease the god's that cursed Alyssa?

When Lysa has Sansa brought to the High Hall to answer for the kiss with Littlefinger...

...Amidst so much white marble even the sunlight looked chilly, somehow . . . though not half so chilly as her aunt. Lady Lysa had dressed in a gown of cream-colored velvet and a necklace of sapphires and moon-stones. Her auburn hair had been done up in a thick braid, and fell across one shoulder. She sat in the high seat watching her niece approach, her face red and puffy beneath the paint and powder. On the wall behind her hung a huge banner, the moon-and-falcon of House Arryn in cream and blue.

...four things stand out in the description of Lysa...

The cream colour of her gown,

The necklace she wears,
Her face,
and her braided hair.

Lysa is eventually pushed to her death through the Moon Door and she tumbles to the Vale below. Although we dont see her fall, we can imagine what she must have looked like when she was falling through the air.  

Unlike the waters of Allysa's tears, Lysa definitely reached the Vale below.

This is what early scientists believed sperm was. 

Credit: N. Hartsoecker, 1695

Antony van Leeuwenhoek may have discovered a new world of cells in seminal fluid, but he was very mistaken about how sperm work to fertilize eggs. In fact, the process of fertilization wasn’t proven until 1879, according to “A Mind of its Own: A Cultural History of the Penis” (The Free Press, 2001). In the 1600s, researchers believed that humans came preformed, curled in miniature inside either the egg or the sperm. “Spermists,” as the believers in the latter theory were called, even claimed to be able to see tiny humanoids inside the head of sperm cells. These spermist argued that women simply provided an incubator for the male seed.https://www.livescience.com/23845-sexy-swimmers-sperm-facts.html

The mammalian sperm cell can be divided in 4 parts:

• head: it contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. It also contains vacuoles.
• neck: it contains one typical centriole and one atypical centriole such as the proximal centriole like.
• midpiece: it has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix, uterus and uterine tubes.
• tail or "flagellum": it executes the lashing movements that propel the spermatocyte. https://en.wikipedia.org/wiki/Sperm#Anatomy

Lysa description looks like a sperm cell,

The tail... her thick braided hair.

The midpiece...  her puffy  powdered face
The neck... her moonstone and sapphire necklace.

The head... her cream coloured velvet gown

Did the first Men perform this sacrifice on the mountain before the Eyrie was built?

Is this the reason the Moon Door is made of weirwood? 

Were people sacrificed through the Moon Door so that house Arryn could conceive children? 

We see evidence of human sacrifice in Westeros.
Craster gives his sons "to the wood"
The bones in the mouth of the weirwood tree at Whitetree, north of the wall.

The white haired lady with the bronze sickle in Brans vision,

(Queensgate)Snowgate at the Wall.

Mirri Maz Duur, ......."Only death can pay for life"

Jaqen H'gar......"The Red God has his due, sweet girl, and only death may pay for life."

There is a Native American tribe, The  Multnomah, who have a similar legend of a maiden sacrificing herself by jumping from the  Multnomah Falls to cure the young and weak of a great sickness https://www.firstpeople.us/FP-Html-Legends/ALegendOfMultnomahFalls-Wasco.html

THE JOURNEY

What i'm suggesting is that the First Men once performed human sacrifices at the site the Eyrie occupies now. The sacrifices were carried out in such a way as to represent sperm travelling from male(the Giants Lance) to fertilize the female (the Vale) womb.

The Gates of the Moon- Buttocks/Prostate

Sacrifice- Sperm

Stone- Testicles

The path from the Gates of the Moon to the top of the Giants Lance where Alyssa's Tears flows over the mountainside  - Urethra 

The Giants Lance- Penis

The Vale- Womb

THE GATES OF THE MOON

The prostate,

....The function of the prostate is to secrete a slightly alkaline fluid, milky or white in appearance, that in humans usually constitutes roughly 30% of the volume of semen along with spermatozoa and seminal vesicle fluid. Semen is made alkaline overall with the secretions from other contributing glands, including, at least, seminal vesicle fluid. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. The prostatic fluid is expelled in the first part of ejaculate, together with most of the sperm. In comparison with the few spermatozoa expelled together with mainly seminal vesicular fluid, those in prostatic fluid have better motility, longer survival, and better protection of genetic material.

The prostate also contains some smooth muscles that help expel semen during ejaculation.

https://en.wikipedia.org/wiki/Prostate

The prostate (from Ancient Greek προστάτης, prostates, literally "one who stands before", "protector", "guardian"....

The crescent moon(virgin) protected by House Royce of the gates of the Moon

House Royce of the Gates of the Moon is a cadet branch to the Royces of Runestone. They have intermarried with noble Vale houses, and potentially one of the Great Houses as well, House Stark.

...Even so, it was full dark before they reached the stout castle that stood at the foot of the Giant's Lance. Torches flickered atop its ramparts, and the horned moon danced upon the dark waters of its moat. The drawbridge was up and the portcullis down, but Catelyn saw lights burning in the gatehouse and spilling from the windows of the square towers beyond.

"The Gates of the Moon," her uncle said as the party drew rein. His standard-bearer rode to the edge of the moat to hail the men in the gatehouse. "Lord Nestor's seat.   A Game of Thrones - Catelyn VI

The function of the prostate is to secrete fluid to aid in the travel of sperm through the urethra.

The function of House Royce in this scenario, as The Keepers of the Gates of the Moon, is to get the sacrifice(sperm) from Stone, safely to the top of the mountain.

The sacrifice may have been a bastard, born to a high lord or a King claiming his right to the First Night.

Dressed in cream or white with a long, thick braid in her hair?

The name given to bastards born in the Vale is Stone,

The path  from the Gates of the Moon to the Eyrie - the urethra - ascends the mountainside to the Eyrie.

 The male urethra is a narrow fibromuscular tube that conducts urine and semen from the bladder and ejaculatory ducts, respectively, to the exterior of the body . Although the male urethra is a single structure, it is composed of a heterogeneous series of segments:  1 prostatic, 2 membranous and 3 spongy . The spongy portion(3) is made up of two parts-(bulbar 3a) and (pendulous 3b.) The green Line going north to south in the images below

Where the different segments of the Urethra connect is the waycastles Stone, Snow and Sky.

We can use Catelyn's Journey to the Eyrie as an example of how the Sacrifice (sperm) would travel to the top of the mountain where the Eyrie now sits.

                                           

 When Catelyn arrives at each of these "segments" she swaps the animal she is riding to a new one to journey through the next "segment"

 Catelyn arrives at the Gates of the Moon riding a horse. She is met by the Keeper of the Gates of the Moon, Nestor Royce to begin her journey to the Eyrie,

...Her uncle nodded. "It is too dark to see them, but the steps are there. Too steep and narrow for horses, but mules can manage them most of the way. The path is guarded by three waycastles, Stone and Snow and Sky. The mules will take us as far up as Sky." 

Tyrion Lannister glanced up doubtfully. "And beyond that?"                                                         

Brynden smiled. "Beyond that, the path is too steep even for mules. We ascend on foot the rest of the way. Or perchance you'd prefer to ride a basket. The Eyrie clings to the mountain directly above Sky, and in its cellars are six great winches with long iron chains to draw supplies up from below. If you prefer, my lord of Lannister, I can arrange for you to ride up with the bread and beer and apples."  A Game of Thrones - Catelyn VI

Catelyn meets Mya Stone, who will see her safely to the top of the mountain. Mya assumes the protection of Catelyn from Nestor Royce.   Sidenote- is Mya's mother a Royce?

..."The mules know the way, Ser Brynden." A wiry girl of seventeen or eighteen years stepped up beside Lord Nestor. Her dark hair was cropped short and straight around her head, and she wore riding leathers and a light shirt of silvered ringmail. She bowed to Catelyn, more gracefully than her lord. "I promise you, my lady, no harm will come to you. It would be my honor to take you up. I've made the dark climb a hundred times. Mychel says my father must have been a goat."  A Game of Thrones - Catelyn VI

Catelyn changes from riding a horse to riding a mule for the journey,

...Catelyn took her leave of her uncle and the others as Tyrion Lannister was led off, then followed the bastard girl through the castle. Two mules were waiting in the upper bailey, saddled and ready.  A Game of Thrones - Catelyn VI

When they reach the waycastle, Stone, they change to fresh mules to journey to Snow,

...Then it was up onto a new mule and out again into the starlight. The second part of the ascent seemed more treacherous to Catelyn. The trail was steeper, the steps more worn, and here and there littered with pebbles and broken stone.  A Game of Thrones - Catelyn VI

At Snow, Catelyn is given a white mule to ride the rest of the way to Sky,

 ..."We ought to keep going, my lady," she said. "If it please you." Catelyn nodded.                             Again they were given fresh mules. Hers was white. Mya smiled when she saw him. "Whitey's a good one, my lady. Sure of foot, even on ice, but you need to be careful. He'll kick if he doesn't like you."  A Game of Thrones - Catelyn VI

A mule is the offspring of a male donkey  (jack) and a female horse (mare).  Horses and donkeys are different species, with different numbers of chromosomes. Mules and hinnies have 63 chromosomes, a mixture of the horse's 64 and the donkey's 62. The different structure and number usually prevents the chromosomes from pairing up properly and creating successful embryos, rendering most mules infertile.

When the Journey reaches the waycastle Sky,

 ..."The last part is inside the mountain. It can be a little dark, but at least you're out of the wind. This is as far as the mules can go. Past here, well, it's a sort of chimney, more like a stone ladder than proper steps, but it's not too bad.  A Game of Thrones - Catelyn VI

From Sky to the Eyrie

...The Eyrie was the only castle in the Seven Kingdoms where the main entrance was underneath the dungeons. Steep stone steps crept up the mountainside past the waycastles Stone and Snow, but they came to an end at Sky. The final six hundred feet of the ascent were vertical, forcing would-be visitors to dismount their mules and make a choice. They could ride the swaying wooden basket that was used to lift supplies, or clamber up a rocky chimney using handholds carved into the rock. A Feast for Crows - Alayne I

Catelyns Mode of transport changes again. 

...Catelyn looked up. Directly overhead, pale in the dawn light, she could see the foundations of the Eyrie. It could not be more than six hundred feet above them. From below it looked like a small white honeycomb. She remembered what her uncle had said of baskets and winches. "The Lannisters may have their pride," she told Mya, "but the Tullys are born with better sense. I have ridden all day and the best part of a night. Tell them to lower a basket. I shall ride with the turnips."  A Game of Thrones - Catelyn VI

The winch that lifts the basket is pulled by Oxen,

Mord took up his whip and cracked it, and the first pair of oxen began to lumber in a circle, turning the winch. The chain uncoiled, rattling as it scraped across the stone, the oaken bucket swaying as it began its long descent to Sky. Poor oxen, thought Alayne. Mord would cut their throats and butcher them before he left, and leave them for the falcons. Whatever part remained when the Eyrie was reopened would be roasted up for the spring feast, if it had not spoiled. A good supply of hard frozen meat foretold a summer of plenty, old Gretchel claimed. A Feast for Crows - Alayne II

Like Mules, Oxen are also infertile.  Oxen are commonly castrated adult male cattle; castration makes the animals more docile,

A castrated male (occasionally a female or in some areas a bull) kept for draft purposes is called an ox (plural oxen); "ox" may also be used to refer to some carcase products from any adult cattle, such as ox-hide, ox-blood or ox-liver. beef2live.com definition

The sacrifice (sperm) reaches the top of the mountain now the site of the Eyrie to travel through the Moon Door to the Vale below.

..."Only death can pay for life, my lord. A great gift requires a great sacrifice."

"Where is the greatness in a baseborn child?"

"He has kings' blood in his veins. You have seen what even a little of that blood could do—"  A Storm of Swords - Davos V

Sterile Mountain

Alyssa's curse may be the cause of the apparent infertility of House Arryn. In the legend the gods cursed her. But the old gods may have been angry with the Arryns already. Because of where they built their castle.

.

Legend claims it was his future wife, Lord Hunter's daughter Teora, who reminded him of how his grandfather had defeated Robar Royce, by attacking from the high ground. Much taken by the girl's words, and by the girl herself, Lord Roland resolved to seize the highest ground of all and decreed the building of the castle that would become the Eyrie. The World of Ice and Fire - The Vale: The Eyrie

 The six hundred feet peak from Sky to the Eyrie represents.... the 'mast' (as GRRM likes to say).
To get to the top you have to go inside the mountain.


 Dawn was breaking in the east as Mya Stone hallooed for the guards, and the gates opened before them. Inside the walls there was only a series of ramps and a great tumble of boulders and stones of all sizes. No doubt it would be the easiest thing in the world to begin an avalanche from here. A mouth yawned in the rock face in front of them. "The stables and barracks are in there," Mya said."The last part is inside the mountain. It can be a little dark, but at least you're out of the wind. This is as far as the mules can go. Past here, well, it's a sort of chimney, more like a stone ladder than proper steps, but it's not too bad. Another hour and we'll be there." A Game of Thrones - Catelyn VI



The Blue Gate

To get to this 'chimney' you would have to walk through the 'yawning mouth' in the rock face,


"Then pass," the door said. Its lips opened, wide and wider and wider still, until nothing at all remained but a great gaping mouth in a ring of wrinkles.  A Storm of Swords - Bran IV




When Bran and company reach the Nightfort, they see a small weirwood,

The Reeds decided that they would sleep in the kitchens, a stone octagon with a broken dome. It looked to offer better shelter than most of the other buildings, even though a crooked weirwood had burst up through the slate floor beside the huge central well, stretching slantwise toward the hole in the roof, its bone-white branches reaching for the sun. It was a queer kind of tree, skinnier than any other weirwood that Bran had ever seen and faceless as well, but it made him feel as if the old gods were with him here, at least.. A Storm of Swords - Bran IV


In my opinion these are the branches of the weirwood tree the Black Gate is carved into growing through the earth above the Black Gate.



If the Black Gate was removed from beneath the Nightfort, Sam and Gilly's journey to the kitchen where they meet Bran, would be similar to the 'stone chimney' route from Sky to the Eyrie.

A yawning mouth in the wall where the weirwood gate used to be.

Leading into the well that ascends to the Nightfort.

 The 'yawning mouth' entrance to the cave at Sky looks like the Black Gate does but with the weirwood gate removed.

The Blue Gate.

The Black Gate is called 'black' because only a man who has 'taken the black' can open it.

"You won't find it. If you did it wouldn't open. Not for you. It's the Black Gate." Sam plucked at the faded black wool of his sleeve. "Only a man of the Night's Watch can open it, he said. A Sworn Brother who has said his words." A Storm of Swords - Bran IV

Some think for the was for the purpose of sacrifice.


The Blue Gate would be used by someone 'taking the blue'.

And your father … he must have good reasons for packing you off to the Night's Watch …"

"Stop it," Jon Snow said, his face dark with anger. "The Night's Watch is a noble calling!" A Game of Thrones - Tyrion II

'The Blue' also calls at the Eyrie.

Gods save me, some previous tenant had written on the wall in something that looked suspiciously like blood, the blue is calling. At first Tyrion wondered who he'd been, and what had become of him; later, he decided that he would rather not know.

If only he had shut his mouth …  A Game of Thrones - Tyrion V

"Men were not meant to leave the earth. Spend too much time in the clouds and you never want to come back down again. I know skinchangers who've tried hawks, owls, ravens. Even in their own skins, they sit moony, staring up at the bloody blue."  A Dance with Dragons - Prologue

This gate/tree being removed could be seen as sort of vasectomy. Severing the weirwood from its roots in the mountain.

Vasectomy is a surgical procedure for male sterilization or permanent contraception. During the procedure, the male vas deferens are cut and tied or sealed so as to prevent sperm from entering into the urethra and thereby prevent fertilization of a female through sexual intercourse. https://en.wikipedia.org/wiki/Vasectomy

The removal of the tree/gate would be cutting the vas deferens.



The vas deferens (Latin: "carrying-away vessel"; plural: vasa deferentia), also called ductus deferens (Latin: "carrying-away duct"; plural: ductus deferentes), is part of the male reproductive system of many vertebrates; these ducts transport sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation. https://en.wikipedia.org/wiki/Vas_deferens




Someone could still climb the mountain and perform the sacrifice but it wouldn't have the same meaning or the same' potency'

                                  With the Gate                                  Gate removed                        

What happened to the tree then?

The wood from this tree/gate could be what was used to make the carved weirwood throne of the Arryn's.

The wretched boy had started it, looking down on him from a throne of carved weirwood beneath the moon-and-falcon banners of House Arryn. A Game of Thrones - Tyrion V


And the Moon Door.

The press of spectators parted. A narrow weirwood door stood between two slender marble pillars, a crescent moon carved in the white wood. Those standing closest edged backward as a pair of guardsmen marched through. One man removed the heavy bronze bars; the second pulled the door inward. Their blue cloaks rose snapping from their shoulders, caught in the sudden gust of wind that came howling through the open door. Beyond was the emptiness of the night sky, speckled with cold uncaring stars.

"Behold the king's justice," Lysa Arryn said. A Game of Thrones - Tyrion V

 House Arryn may have been warned that the old gods would curse them if they removed the weirwood tree/gate from the mountain. This may have been why they tried to build a godswood at the Eyrie.


Lysa's apartments opened over a small garden, a circle of dirt and grass planted with blue flowers and ringed on all sides by tall white towers. The builders had intended it as a godswood, but the Eyrie rested on the hard stone of the mountain, and no matter how much soil was hauled up from the Vale, they could not get a weirwood to take root here. A Game of Thrones - Catelyn VII



 When Sansa opened her eyes again, she was on her knees. She did not remember falling. It seemed to her that the sky was a lighter shade of grey. Dawn, she thought. Another day. Another new day. It was the old days she hungered for. Prayed for. But who could she pray to? The garden had been meant for a godswood once, she knew, but the soil was too thin and stony for a weirwood to take root. A godswood without gods, as empty as me. A Storm of Swords - Sansa VII  


When they couldn't get a weirwood to take root they may have tried to 'simulate' the sacrificial ceremony by constructing the Moon Door as a way of honoring or appeasing the Old gods

Both Catelyn and Sansa mention the soil being too thin and stony for a weirwood to take root. This may be so, but...

The call came from behind him, softer than a whisper, but strong too. Can a shout be silent? He turned his head, searching for his brother, for a glimpse of a lean grey shape moving beneath the trees, but there was nothing, only . . .

A weirwood.

It seemed to sprout from solid rock, its pale roots twisting up from a myriad of fissures and hairline cracks. The tree was slender compared to other weirwoods he had seen, no more than a sapling, yet it was growing as he watched, its limbs thickening as they reached for the sky. Wary, he circled the smooth white trunk until he came to the face. Red eyes looked at him. Fierce eyes they were, yet glad to see him. The weirwood had his brother's face. Had his brother always had three eyes?  A Clash of Kings - Jon VII

It's uncertain how a weirwood grows. All the weirwoods in the story are said to be ancient. We do see a weirwood tree growing from solid rock in a dream that Jon has. But whether this really is the way they grow isn't clear. (to me anyway)

The reason a weirwood will not grow at the Eyrie may be because the soil is thin and stony as Sansa believes, or because the Eyrie rests on the hard stone of the mountain as Catelyn believes.

Or it could be that there was already an ancient weirwood that had grown through the heart of the mountain to pierce the top of the Giant's Lance. An old god that was ripped out by the Arryns to make way for the monument to the Seven that stands there now.

Seven towers, Ned had told her, like white daggers thrust into the belly of the sky, so high you can stand on the parapets and look down on the clouds.  A Game of Thrones - Catelyn VI

 Maesters will tell you that the weirwoods are sacred to the old gods. The singers believe they are the old gods.  A Dance with Dragons - Bran III

 A godswood without gods, as empty as me. A Storm of Swords - Sansa VII


Swords Of Ice And Fire

Who's Looking Through The Black Gate

Aerys,Tywin And A Bride For Rhaegar

The Trident Has Three Heads

Davos's Thumb

Coin Well Spent

Valonqar - High Valyrian Or Bastard Valyrian?

Brandon's Bastards