It would be easier for you to just YouTube it than for me to describe it to you. After entering the cave through the waterfall there will be what looks like a sheer drop into a crevice on your right side but there is actually a narrow path down. Head down it and follow that shaft and eventually you'll find the treasure. You'll have to do some careful maneuvering and jump up a ledge at one point if I remember correctly, but you should figure it out easy enough.
