At the end of Morgan's Leap is a second jumping puzzle, Dark Reverie, which is much harder, it's filled with some nightmare court and plants and stuff and you can only open the door to that section from the inside - so if someone is in, they can let you in, otherwise you've got to complete Morgan's leap first to access the nightmare court section (and if you fail at the puzzle, you fall down and die, and have to repeat morgan's leap again). So at the end of the second climb is a second chest and the dark reverie achievement.. I think that's what you're talking about anyway