The Eyrie
The ancient seat of House Arryn, one of the oldest lines of Andal nobility. It is situated in the Mountains of the Moon astride the peak known as the Giant's Lance, several thousand feet above the valley floor below. It's considered impregnable to attack. During winter years, the Arryns seek refuge against the cold at the base of the mountain in the Gates of the Moon.
The Castle
The Eyrie is the smallest of the great castles, consisting only of a cluster of seven slim, white towers bunched tightly together. They can hold up to five hundred men. The castle is made of fine white stone. The towers encircle a garden, which had been meant as a godswood, but no weirwood tree would take root in the stony soil. The barracks and stables are carved directly into the mountain. Though it is a small castle, the granary is as large as those found in much larger castles, like Winterfell.
The High Hall of the Arryns is where the household takes meals. It is a long and austere hall, with walls made of blue-veined white marble. At the end of it sits the throne of the Arryns, a seat carved of weirwood. It has narrow, arched windows, between which are torches mounted on high iron sconces.
Moon Door: In the High Hall there is a narrow weirwood door that stands between two slender pillars. A crescent moon is carved into the door. The door opens inward, and is barred by heavy bronze. The door opens into the sky. Most executions at the Eyrie use this door, which opens onto a six hundred foot drop to the stones of the valley below.
The Crescent Chamber: The Eyrie's reception hall. Here, guests are given refreshments and warmed by the fire after making the climb up the Giant's Lance.
The Maiden's Tower: Easternmost of the seven towers of the Eyrie. From a balcony on the tower, one can see the Vale and the Giant's Lance.
Sky Cells: The Eyrie's dungeons are particularly infamous; they are merely shelves on the side of the mountain's sheer cliffs, left open to the cold sky. Many prisoners, driven mad by the cold and howling wind, commit suicide rather than remain imprisoned.
Mountain Defenses
To reach the Eyrie, an invading army would have to overcome the Bloody Gate guarding the High Road, then overcome the Gates of the Moon located at the bottom of the mountain and climb up the narrow goat trail. Under normal circumstances this would take half a day, all the while being exposed to attack from the defenders in the Eyrie and its three waycastles along the path:
Stone, the first waycastle. The path to it is surrounded by forest. It has a massive ironbound gate. The stone walls are crowned with iron spikes and its two fat round towers raise above the keep.
Snow, the second waycastle. The trail to it is steeper than that of Stone. It consists of a single fortified tower, a timber keep, and a stable placed behind a low wall of unmortared rock. It is nestled into the Giant's Lance so as to command the entire pathway from Stone to Snow.
Sky, the third waycastle. The path to it is treacherous. It is open to the wind and the steps are cracked and broken from the constant freezing. Sky is a high, crescent-shaped wall of unmortared stone raised against the side of the mountain. Inside the walls are a series of ramps and a great tumble of boulders and stones of all sizes, ready to throw down or even cause a minor avalanche. There is a cavern containing a long natural hall, stables, and supplies. Handholds carved into the rock lead to the Eyrie, while earthen ramps give access to the walls. The Eyrie is located six hundred feet above this point.