The Jedi

In the room before the one you describe where you first saw the megapedes fighting there is flaming skull thingy on the ceiling hit it with a spear and it will fall down to ignite a pot light a spear on the pot and throw it through the whole in the wall to the left of the waterfall (since if you go under the waterfall the spear will be extinguished) then go around and get the spear. (be sure to walk on the edge of the water)