You're almost done, but the worst part is still coming. From the big chest, move the blocks to the right to get to the door. The next room has a spider door, do not go through it yet. Go right first. The door shuts on you and there is a Fire Fairy in this room as well as a bunch of Babusus. Find the key under the skull directly north of where you entered the room. The switch to open the door is under the skull northeast of the Guruguru Bar. Go south, avoid the Guruguru Bar in this room and go left. The switch under the skull reveals a chest with yet another key. You might have as many as 3 now, which is fine. Better too many than too few. Backtrack a couple of rooms until you are in the room with the spider door, go through it.