I'm currently on the monkey finding quest thing.. I'm on this bit and the guide says to;
'Use your boomerang to rotate the bridge and then rotate it again while on it. This will connect the bridge to two additional paths. Enter the door on the East side search for the next monkey. After entering, you'll see three holes in the ground, two of which are covered by cobwebs. Equip your lantern while standing on the left one to burn it away and fall to the caged monkey below. Just bat at the cage with your sword to free the monkey and then climb the vine covered tree roots to the top level. Exit the room through the way you came in.'
But I walk over the bridge behind the chest I found the key in, and then the monkey isn't there for me to follow him.