The vast Underdark beneath Faerûn's surface is a deadly world whose inhabitants (even formidable beasts and races armed with both ruthlessness and fell magic) band together in fortified cities to survive. It's difficult to map on flat parchment because of its layers and sloping tunnels. Local control over specific locales may change with bewildering and deadly rapidity.
Many small "governed" areas of the Underdark never appear on any maps. Liches are the worst sort of this kind of minor ruler. With their dark humor and arrogance, liches to refer to their domains as "dooms." The equivalents of these undead human wizards, such as the illithid alhoon and elven baelnorn, also rule small Underdark domains.
Most lich dooms feature hiding places for magic (crevices or high ledges) and a complex tangle of passages and caverns. Liches use abandoned dwarven and gnome delves that have useful rooms and doors, if clearances are sufficient and no traps were left behind.
Araundordoom is a typical doom, ruled by the lich Araundor. Once a human wizard of Mulhorand; he long ago dwindled into a near-skeletal state and lost the last vestiges of sanity. He now exists to destroy intruders, gloat over their sufferings and seize any magic they carry. He uses spells to read the thoughts of approaching creatures and even to steal memorized spells right out of their minds. Intruders' deeds, aims, and desires both entertain him and give him weapons against them. He can use names thus gleaned to pose as a friend or acquaintance crying for aid to lure creatures into his traps.
Like most liches, Araundor prefers to avoid crushing traps that could harm him. He employs poisons in the pools of water found in his doom, places leg-hold snares where intruders must wade then immerses himself either underwater in the deepest pools (to avoid hostile fire magic) or in sucking mud through which intruders must struggle. His silent or stilled spells can be unleashed unimpaired from within the murk or muck.
Araundor loves to taunt foes, revealing what he knows about them and goading them into anger, fear, and recklessness - but he's smart enough to do so when only one or two opponents remain active. He animates several corpses and skeletons of past intruders to pose as himself and cause intruders to waste magic. The patient use of ruses and attacks, coupled with the labyrinth he has chosen as his doom, let him scatter bands of foes so he can deal with them one or two at a time.