Occasionally, if a Mines filler level generates where there is a sufficiently large space of empty stone, a little separate walled-off area may generate disconnected from the main map, containing a few gnomes and dwarves, and some more gems and gold, possibly in a chest. This area won’t get the stairs generated in it, and should probably contain a hole so that a randomly teleporting player won’t get stuck there (other types of escape items could get picked up by the gnomes and dwarves).