Then head back to the main cavern to unlock the door at the back of it. Kill the drowners to claim the Laboratory Key at the bottom of the pool.
Turn the levers so that they're all facing in to the small area between them all and a pool of water will open up. Once you've done so exit out the left side of the cavern and you'll come to a room with some statues. Go inside, dispel the illusion, and you'll have a Golem to fight. If you head around to the west of the island and hug the outside of it as you head north you'll find a path that leads down to a cave. On Temple Island there is a hidden cave to the northwest of the island. A bit more legwork for this collection of diagrams.
