Fishtown: the entryway, lots of spies for lower level folk and people too smart or not able to descend deeper. Named for the nickname for new inmate delvers.
The Tin Altar: a working tin mine, a place to earn a meal and some water for a day’s dangerous work. Underdark slavers often purchase prisoners here.
Barrows: so many people have buried their dead here, now the inmates do so, lots of graffiti and ghouls
Gallows: these are the crpyts where the arch-mage’s wraith-muscle, the hanged men rest when they are not floating through the dungeon, doing his bidding. Some say the Hanged Men are the remnants of powerful guard/apprentices. There is a ritual to be done to summon them at the threshold, going further in is folly, a place where even the most foolhardy probably won’t chase you.
When the Hanged men drain you of a level, it becomes a black gem. If you carry your own gem, you retain the level but the only way to get it is to pry it from the wraiths’ eye-sockets. For a few hundred GP per level, an alchemist can grind the gem into dust and get it right back into your body.
The Manse: hidden by powerful wards, said by some to be the deepest level and by others to be a pan-dimensional sub-level; it is the arch-mage’s sanctum, said to have once been a seclusium.
Crowpit: it is a (said to be) bottomless pit with crow-cages floating in it, said to be the work of an ambitious guard-apprentice when the dungeon first became re-tasked as a prison. Summoning infernal powers is easier here, as is necromancy.
Prentice City: This is an abandoned dwarven fort held by a joint effort between the Guild and the guards. The Dwarves were destroyed by a Quaggoth rampage centuries ago, when the mines here still spit out iron and gems. It is also called the Barracks and the Guildhouse.
Dozen Altars: Also known as Ghoultown, Dozalt and Altar. This is a labyrinth of tunnels and catacombs, broken temples to slumbering deities and ghouls. A demon-god of ghouls is on the rise down here, hissing threatening curses at Prentice City, threatening to take it. The demon-god’s anointing ceremony involves biting and cannibalism.