Roguelike games, like Angband, Nethack and the like, are dungeon crawls that are heavily influenced by D&D; actually, they are rather like what I imagine early wargame-esque D&D to have been: a primarily tactical exercise in which the player-character tries to explore a dungeon, survive, kill things, and take their stuff. The player is quite divorced from their own character and sees him/her more as a "piece" moving around the game world than as an actual person with hopes and fears and relationships. When the character dies, the player shrugs and starts over with a new one. "This time, I'll be a wizard."
One of the innovations that roguelikes have introduced is the Dungeon Town. In -band games (-bands, like Angband, Zangband, and ToME, are a subdivision of roguelikes stemming away from the (inferior, in my view) -hacks, like Nethack), dungeons are infinitely regenerating. Each time you enter level 1, it's a different level 1, created randomly. But every so often you come across a permanent fixture - a dungeon town. These are always generated randomly for their initial spawning, but after that they remain in place.
Dungeon towns are, as the name suggests, safe havens within the megadungeon where the player can rest, recuperate, and buy supplies. Often, they have rare shops selling specialist items at a high markup. They are always a boon to the player, as they allow him to get hold of essential emergency goods such as food and scrolls of word of recall if he has lost his supply.
I like the idea of dungeon towns. Anything that suggests that the dungeon has a meaningful ecology, economy and political sphere is intrinsically interesting to me, and the dungeon town points to all of those things: there are intelligent things living in dungeons, and intelligent things both cooperate with each other and also show a natural predisposition towards trade. It stands to reason that there would be a considerable amount of the latter going on between dungeon towns, especially, but also with the outside world. In such an environment, the PCs, as outsiders, would be traders as well as adventurers - taking out what the dungeon has in great abundance but also bringing in items from the outside that are of great value to the dungeon dwellers. (Who knows what a dungeon dweller would pay for dried fruit, a donkey, spices?)
When we say "dungeon town", of course, we shouldn't be thinking of a load of houses and shops incongruously nestled between the Pit of Fire Drakes and the Lair of the Grell Queen. A dungeon town might be a set of tunnels a group of Duergar have made their fortress; a deep-gnome warren; an encampment of mongrelmen in a vast cavern; whatever - somewhere where trade can be carried out and (brief) respite found.