The Demon Hall was drawn as a drop-in set of two levels meant to be stuck into another dungeon on-the-fly (like when running a solo game using the rules from the 1e DMG or the Labyrinth Lord version from Ruins of the Undercity).
The two levels are linked together and centred around the Demon Hall itself, a massive two-level hall with a second-level mezzanine.
The upper level of the Demon Hall opens up on the upper mezzanine of the Demon Hall itself. Railings look over the eastern end of the lower level, including the dais. The stairs up from this level connect to the dungeon above, while both stairs down (or climbing or jumping from the mezzanine to the main floor of the Demon Hall) lead to the lower level of the Demon Hall map.
The lower level of the Demon Hall includes significantly more side rooms and chambers than the upper level. There are two stairways up to the upper level map, and a single stairway (immediately facing one of the stairs up to the level above) that leads down further into the dungeons where the Demon Hall has been inserted.
The Demon Hall maps were drawn in pencil on plain white paper around four years ago, lost, found, scanned and contrast-enhanced for your viewing pleasure.