The Ultimate Dungeon is an 11-level dungeon that becomes accessible after closing the Chaos Gate. It can be entered only once by using the weird fire starter on a dormant volcano. The first 10 levels have random layouts. The final level has a predefined layout with a horde of difficult monsters. The supreme balor, located on the final level, drops the scroll of omnipotence when killed.
All monsters generated in the Ultimate Dungeon are generated at a high level. On the first level monsters are generated at around level 20; on the final level they are generated at around level 50. The first 10 levels can be generated cavernous, magma-filled, or littered with bones, in addition to standard random dungeon features.
The final level has a fixed layout. The left side features random, dangerous monsters, and the chamber on the right has the supreme balor, three greater balors, six balors, and a group of molochs that can include emperor molochs. The supreme balor drops the scroll of omnipotence. Emperor molochs found here will drop crumpled scrolls.
There do not appear to be any quests the require visiting the Ultimate Dungeon. However, the purpose of the scroll of omnipotence is still unknown.