In the far eastern room there is lever socket on the ground. There is not a huge reward, though.
It lifts up a false wall, to reveal a room with crappy loot, IIRC.
In the southern tunnel, the western branch has a hidden room at the end. I don't recall anything extra at the far southern end, though.
face south at the end of the room, and a button is hidden behind the curtains to the left. In that room there is another button behinds some crates to the left, which will open another door, but seal the first; use the dragon stone to get out.
