I won't go into all the details. Basically, you need to run around many times collecting bombs.
Use the befuddlement gas at A, and leave it there for future use.
To get the key, use the pickaxe at B to cover up the teleporter. Drop the pickaxe at B before you drop down, though, because you'll need it later.
Make sure there's a monk at C every time you teleport into that area. Kill monks as necessary.
To get to the exit, first drop the key at D. Then leave the area, get the pickaxe, and return. Light a bomb at E, and use the pickaxe to fill in the gap in the floor created by the bomb.