The Citadel

The Citadel is the premier military academy within the Hyperion Empire. It is the location where the most elite, secret regiments are trained, including the Blue Elves, Wyvern Riders, and Mithral Guard.
The Citadel is located within the [name of lake], a landlocked sea west of Mornage. It sits on the one of the only, and the largest, islands in the sea, far isolated from the coast, and it is shielded from teleportation magics save for a single sigil that only the Sovereign's Council is able to access. As a result, there are only two ways in: with an airship through the highly restricted airspace, or by boat from [town]. This isolation is twofold: First, it helps protect the Citadel from invaders that may seek to either gain access to the secrets within or lay waste to it; second, it prevents those taken against their will from escaping, at least not easily.
The Citadel is made out of a dark gray stone mined from quarries in Treifenburn, giving a gloomy, almost forlorn appearance to it. It is easily recognizable by its square towers that jut into the sky at differing heights. Very few windows are visible from the outside, and those that can be seen are frequently left dark no matter what time it is, leaving an air of abandonment to the facility. A large central spire of the Citadel is where most learning takes place, with the other towers reserved for practical training or dormitories. At the ground floor is a great hall of a dining room. In a hollowed out area in the bottom is a large aerie sort of area for the Wyvern Riders. This is where they leave their Wyverns when they are practicing different skills or are learning from books.
The lake it lies in is a sort of crater, surrounded on all four sides by mountains. It is suspended by many magical chains and with reisstone on the bottom, floating in the air with the only way of getting from land to the castle being a stone bridge with a large, wrought iron gate. This gate is constantly manned by a contingent of soldiers with a tower to either side and two more halfway between the land and the Citadel. Another path runs along either side of the bridge up and down the entire length, allowing guards to constantly patrol to stay vigilant.
At any given time, there are at least five hundred servants, three hundred guards, and nearly a thousand students among a hundred instructors. During times of war or particular strife, these numbers will increase drastically as the Hyperion Empire aims to churn out a larger army.