Stuck on L9
The long staircase is the "skeleton key" staircase – each time you use a
skeleton key, another entrance into that staircase opens up. It's a handy way
to get from the lower levels back to level 4 (food/practice) quickly. As for
the room with the gate/lever, your explorations should have shown you a couple
of staircases (one up, one down). Hint: They don't go to regular levels; if
you've already dropped the chest into the pit (using the lever), try going
"downstairs" …