Demon Helmet Quest
Step 1 Enter the cave north of Edron
The way in is the hole at 33163,31636 on the surface north of Edron - the same cave that leads to the Edron annihilator. From there the route runs 33161,31624 (floor 8), 33136,31593 (9), 33169,31588 (10), 33150,31595 (11) and 33144,31589 (12) down to floor 13. Bring a rope: on the way back you climb the ladder at 33144,31589 on floor 13 and use the rope spots under the holes. The stairs at 33250,31697 lead into Cyclopolis, the cave of the Behemoth Quest, and reach neither quest.
Step 2 Two players hold the switches
Two stone tiles at 33190 and 33191 (y 31629, floor 13) work together: while a player stands on each, the wall at 33210-33212, y 31630 is gone. The tiles never change their look, and the wall comes back the moment either player steps off - so a third player has to walk through. The players on the tiles do not have to wait for the way back: the exit does not lead through the wall (see the last step).
Step 3 Through the level 100 gate and the door
The way to the wall leads north from the corridor at 33211,31641 (floor 13): through the gate of expertise at 33211,31638, which needs level 100, a room with fire elementals and the door at 33211,31634. On Mortha that door is not locked - no key is needed.
Step 4 Pull the lever in the chamber
The three chests at 33313 (y 31591, 31592, 31593, floor 15) are walled off until the lever at 33330,31591 is pulled - it removes the red shrine stone standing in the way. The chests carry different quest numbers, so one character takes all three. The same lever opens a magic forcefield at 33316,31591 that takes you straight back to the room behind the door (33211,31636, floor 13) - outside the wall, so the way out does not need anyone on the tiles.