There is a room that has one of the troglodytes for an optional objective. There are two levers that need to be operated to open the door. The first is down the hallway to the left of the "T"-shaped intersection and in an alcove hidden behind a breakable box. Once you operate that lever, return to the hallway you came from and look in the newly opened alcove to the right. There is the second lever which opens the door across from where you first entered the intersection.