Vibrating square
The vibrating square is special location found at the very bottom level of Gehennom. If you perform the invocation ritual when standing on the vibrating square, the entrance to Moloch's Sanctum will be created.
The vibrating square is the square where the invocation ritual is to be performed for entry into Moloch's Sanctum. It is always located on the last dungeon level of Gehennom; therefore, there is no staircase leading down on that level. Only the Sanctum level has a higher dungeon level number.
Identification
The only way to locate the vibrating square is to move over it, at which point you will notice a strange vibration under your feet. This will still occur even if you are mounted or levitating. It cannot appear near the edge of the screen nor the staircase, because there must always be room for the ring of fire traps and water to appear around it.
Many players will mark the vibrating square by leaving an object on it once they have located it. Objects on the vibrating square will not move and the vibrating square itself never changes location.