The path to The Door to Nowhere contains massive moving skulls, pools of water and the aforementioned door, though it is locked.
You must not shoot the rocket fuel or liquid oxygen tanks!!! Continue past soul lamp one to reach soul lamp three.
Push all of the balls down the holes to release Kweek.
Hope you took my advice so you could use the Roofus telepoint as a checkpoint! Climb up the ladders carefully and switch to Chang.