|“||The only way in or out was from the air...||”|
The Citadel is a huge tower that stands out from all the other buildings in the Nest. While other towers are crumbling, overgrown, and made of darker stone, the Citadel is strong, white, and rises above all else. It is the only building tall enough where, on the roof, one can see over the Nest's impassable natural walls. The Citadel appears seamless and smooth, lacking the defined lines of brick and hewn blocks that define the look of every other structure nearby. Its overall shape is reminiscent of a King chess piece.
As Trico is unable to fly, the Boy realizes that the best way to escape the valley's insurmountable walls is to get to the top of the massive tower in its center. The bridge leading to this tower partially collapses under Trico's weight and, the way is blocked by several talismans, stained-glass eyes which Trico fears. So the Boy navigates rotting beams and narrow ledges to get to where he can remove these obstacles. However, a huge army of Armored Knights ambushes the Boy before he can release the levers. Trico initially remains in a bewildered trance but, his love for the Boy overcomes his instinctual fear and he charges to the rescue, saving the Boy but further damaging the bridge. The two barely escape death by miraculously gliding to a nearby tower using Trico's partially-healed wings.
With the main bridge no longer an option, the two choose climb a series of structures and use their height to glide over to the front of the Citadel, laying waste to the Knights guarding it. They eventually find the chamber containing the Master, giving them access to the tower's wide, open roof. Boy and Beast explore its surface. Not finding a connection between it and the nearby valley wall, they see they must fly. But before they are able to escape, the Master summons every Armored Beast in the whole of the valley and causes them to attack and subdue Trico. The Boy manages to destroy the Master and break its control over the enslaved creatures; those flying through the air suddenly fall from the sky. Although sorely wounded, Trico takes the unconscious Boy in his mouth and runs off the tower's roof, amazingly taking flight. He uses what strength he has left to return the Boy to his village.
Some time later, the Boy, now a man, reveals the mirror to the children of his village, shining its light out into the deep night sky. In the final cutscene, it is shown that the Citadel still stands proudly above the valley, although the evil it once contained is gone forever.
The Citadel has two exterior locations. The first is its front gate and courtyard. In addition to a large portcullis, a many smaller doors allow the rapid deployment of Knights to defend the courtyard. Next is the rooftop, which is wide and flat with a broadcast "antenna" which the Master uses to control its subjects. Here there is also shrine where the Armored Tricos deposit the Master's sustenance: children.
Once past the portcullis, there are curving hallways, large dome chambers, a room with a bottomless hole and, two elevators. Higher up there is the Master's chamber, suspended in a cavernous room carpeted with broken barrels. Above the Master is a spinning fan and then the roof access. Most of the rooms are cold and misty, glowing with a soft blue light.
The only way to access the building by foot is by a rickety wooden bridge that can barely support Trico's weight (in fact, it almost completely collapses when he walks on it). The bridge is barred by two talismans and, the bridge is defended by long-range attacks against anyone who approaches. The portcullis can only be opened with the mirror.
The Citadel hosts a large army of Knights and likely serves as their headquarters. They can rapidly deploy to any part of the tower through the mysterious blue doors. Armored Tricos can also be called to defend the tower.