I was going through the maze section of the Citadel, the hall that goes North right after going through the room filled with traps, and behind the North wall in the corner is a Dead Imp. There is torch light glowing on the wall, too, and because I'm playing on Hardcore, there are about 6 or 8 red dots on the minimap moving around in the black area beyond the wall.
I admit, I exploited the game's displacement issue that can be caused by alt-tabbing and going back to the game multiple times to phase through the wall in the corner. I went up and around the wall of this closed-off area till I could get to a spot where I would be able to phase-through again (the position shifting seems to always move your character to the left). It took me into a small room filled with skeletons and some bodies, torches lining the walls....but the visible area would only appear around my character, and the fog of war never lifted when I moved around. There was also a Stone Gargoyle in the room who dropped a Crystal Ball. When I went down to the Imp, Deathknight said "Could this be the annoying Imp we encountered recently?"
I'm curious if this is an unused area or if I just stumbled upon an area that is accessed later in the game that just happens to be in the same data space as the Maze map.