On the far side of the auditorium, you see when up close that the metal door in the SE corner remains quite sound. Tapping it reveals it to be quite thick.
In addition, it is locked.
The larger double doors however, are not locked.
When cracked open and peeked through you see a larger irregularly shaped chamber.
The northeast wall of this room has partially fallen; through it is revealed the dark, murky waters of the pond outside.
Moldering training dummies and other similar equipment hint that this room may have once been a training area for the guards.
In the northeast part of the room, the floor around a dark, jagged hole is surrounded by black scorch marks. Winches and fallen pullys suggest that this is the lift used to lower people into the lowest dungeons.