How do I get out of the Dark Halls?

Hint 1 of 7:

Look for a large circular room full of ghosts.

Hint 2 of 7:

You need to create an explosion in here.

Hint 3 of 7:

Take a look at your automap.

Hint 4 of 7:

One of the niches in the wall of this room is less sturdy than the others.