At the top of the Chasm, past the Bristleback Pen, and across a bridge, is a small area guarded by two Rieklings. Towards the back of this area is an unlocked Boss Chest, and behind that is a skeleton lying next to a leveled shield and mace.
There is an area at the top of the waterfall in the main antechamber. It is possible to reach however there is nothing up there save a Skeleton with a few gold. The rocks found there have clipping problems and it's possible to fall through the floor, and into the void. (Falling off a cell typically spawns the user back somewhere inside it, however.)