Did you notice you could walk through part of the wall around the chest on the west side of the dungeon?
<span class='standouttext'>Spoiler : </span><span class='spoiler'>move the barrels away from the wall around the key...</span>
The key (quest item) from the Lich cave is for an imp just north west of the chieftain's house, who could not sacrifice gold to the shaman because he lost his key.
