1. Fall down this hole:
2. Go out of the cave, up the stairs, and back inside.
3. Go up the stairs on the east side.
4. Walk north to just above the rock...carefully. Go too far N, and you'll encounter another pitfall.
5. Take the secret passage on the left. Re-enter the hallway, and continue east.
6. IMPORTANT: Even though you are now in the room with chest, DO NOT try to grab it. Continue east, and back into the blackness.
7. Follow that secret passage to come around the outside of the room. Go back in. Now you are on the east side of the chest (behind the boulder) where you can safely grab the loot.