The Castle of Lions is a castle located on an island in an alpine lake on planet Arus. The castle serves as the official residence of the Arusian royal family and the headquarters of the Arusian military and the Lion Voltron Force.
There are at least eight entrances to the castle. A drawbridge provides pedestrian and land vehicle access to the castle. The courtyard has landing pads where spacecraft can land ( and one very large spacecraft is usually docked in the courtyard).  A tunnel connects the castle underground with a network of tunnels in the mountains near the castle.  And, of course, the lions' lairs provide access to the castle underground via tunnels.
The centerpiece of the castle is the main keep. The exterior walls of the main keep are made of some type of metal. The keep has four towers at the corners, and a fifth central tower. The royal apartments, barracks, control room, offices for military and civilian staff, storehouses, conference rooms, and at least one kitchen are located inside the main keep.
The keep also serves as an interstellar spaceship.
The control room is the principal command center for Arus's military. Monitor screens allow Coran and his staff to monitor almost anything happening on Arus and out in space. Five chutes in the control room lead to the launch room in the castle underground.
The courtyard is the area of the castle between the shores of the island and the main keep. It is large enough for medium-sized spacecraft to land.
The underground area has the launch room and the royal tomb.
This room allows the Voltron Force to access their lions' lairs from the castle. It is usually reached from chutes leading down from the control room (although there is likely a maintenance entrance). The chutes open directly above the parking spots of the rail shuttles, so the pilots can drop directly from the chute into the shuttle. In one episode though, the pilots simply dropped down to the floor of the launch room and stayed there for a minute before launching. Five tunnels lead from the launch room into the lions' lairs; the shuttles travel through these tunnels.
This is the tomb where King Alfor (and possibly some of his ancestors) are buried. The Voltron Force first visited the tomb to retrieve the activator keys to the lions , and from time to time they would go down to the tomb to commune with the king.