Ideas for Proper Dungeons

The individual hoard, even one guarded by a draugr, dragon, leprechaun or other such, is but a small adventure, or even just a lucky find in between adventures. Your adventurer happens across it, defeats the guardian, maybe falls afoul of the curse set on the loot, but then that's that. Maybe an evening's entertainment! But we do love more involved adventures, be they ever so chestnut-ty. Only just let them have a rationale.

What was the purpose of the dungeon? Is that purpose still fulfilled by the place?
Did the denizens of the dungeon build it themselves, or did they find it and fill it?
Are the denizens of the dungeon organized? How? Why?
Are the denizens the proprietors of the dungeon or are they in some manner employed by another?

A common trope following Tolkien's Moria is that of the abandoned Dwarvish mine:
The dungeon is a complex of tunnels and shafts dug under a mountain, deliberately, in order to mine ores, gems, truesilver, whatever. At some point the dwarves are set upon and driven out, either by dragons or by orcs or by elder creatures awakened by the deep delvers. Since the dwarves were eaten or driven off, the complex is now the dwelling of a broad array of nasties filling its mazy ways.

A temple complex is a classic sword and sorcery trope. Ardis is chock full of temples, because it's chock full of gods. Quite often there's a good deal of gold, silver and gems involved in the altars, ceremonial gear, offerings, and other accoutrements. Less popular gods are typically less powerful, but their temples tend to be poor. The richly-appointed temples tend to belong to more powerful gods, who can be counted on to have: A) fanatic followers and priests defending the temple B) enchanted or demonic guardians defending the temple C) elaborate traps defending the most sacred treasures D) tombs, either of key priests, prophets or the god itself and E) fabulous wealth for anyone wishing to dare the above along with F) the lasting disfavor of the god itself.

This stuff can be strung out over campaigns beautifully: the party either is tasked or undertakes on its own nickel to rob the precious jewelled idol of Nisshur-Telpec from its temple complex; the job goes down easily but as they travel to deliver or fence the idol they find themselves continually harried by the black-robed, fanatic followers of Nisshur-Telpec, who seem to unerringly find them wherever they go - even after disposing of the idol in whatever way they do. (Perhaps if the party researched and found that Nisshur-Telpec was a god of eternal vendetta, they would have picked another target...)  

A dedicated tomb complex (closely related to the temple, possibly one and the same) works too: especially if the goal was to bury the deceased (or is it!) particularly deep. I have in mind Ardis' ancient history of wizard-wars: think of one of the great god-wizards, defeated and imprisoned in a deathlike state far below a mountain. The tomb becomes the heart of a vast underground - were the tunnels the work of the god-wizards who won? Or were they dug by the minions and descendents of minions to worship and perhaps one day free their master?

More to come as it occurs to me.