In Nethack, the bottom level of Gehennom which can only be reached by performing the invocation ritual on the vibrating square on the level above. It is where the fabled Amulet of Yendor is found.

Map

                --------------
                |............|             -------
          -------............-----         |.....|
          |......................|        --.....|            ---------
       ----....^^^^^^^^^^^.......---------|......----         |.......|
       |.......^---------^.........|......+.........|     ------+---..|
     ---.......^|.......|^.........--S----|..GRAVE..|     |........|..|
     |.........^|..._...|^............|   |...YARD..-------..----------
     |.........^|.......|^.........----   |..........|....|..|......|
     |.........^|.......|^.........|      --.......----+---S---S--..|
     |.........^---------^.........|       |.......|.............|..|
     ---.......^^^^^^^^^^^.........|       -----+-------S---------S---
       |...........................|          |...| |......|    |....---
       ----.....................----          |...---....---  ---......|
          |.....................|             |..........|    |..<..----
          -------...........-----             --...-------    |.....|
                |...........|                  |...|          |.....|
                -------------                  -----          -------

(S's are secret doors)

The room to the left, surrounded by traps (the ^'s), is the temple of Moloch, attended by the high priest who holds the Amulet of Yendor. The goal of the game is to retrieve this amulet and offer it on the altar of your god on the Astral Plane.

Moloch's Sanctum is no-teleport, blocked to magic mapping and ineligible to leave bones files.