How do I get to the next level?

Hint 1 of 11:

Have you explored everywhere?

Hint 2 of 11:

Found anything unusual?

Hint 3 of 11:

What about the lever in an alcove toward the northernmost part of the level?

Hint 4 of 11:

Tried flipping it?

Hint 5 of 11:

Did anything happen?

Hint 6 of 11:

The wall behind you moved!  But there's still not an opening.

Hint 7 of 11:

Maybe you should try again?

Hint 8 of 11:

Flip the lever twice, and a small passage will be revealed.  In the passage
are two more levers.