You've already been directed to the Hall of Legends - most fortresses archived in that thread offer enough information to run a solid dungeon crawl with little need for guesswork on the part of the DM.
I'd like to point out a fort of my own (being careful not to toot my own horn too loudly in the process), Weatherwires, which I feel would work excellently as a dungeon. The entire fort is designed three-dimensionally, with many vast open spaces and large structures forming a sprawling underground city. Pathways are intuitive enough so as not to be confusing in a role playing context, while labyrinthine enough that adventurers could easily get lost inside. Every part of the fortress served a definite function, all the way from the summit of the volcano to the deepest depths. As well, the fort has over a hundred years of history detailed on its walls, and in the thread linked in my sig.
Of course, it doesn't fit your criteria exactly - the dwarves of Weatherwires defeated the clowns (at a great loss to themselves), the monarch never arrived (for reasons detailed in the first post of the thread), and the fortress was never abandoned, technically speaking - but there's no reason nameless evils could not have crept back into it's secluded halls during the interim. Then again, it's not the disorganized subterranean sprawl you find in most forts, so perhaps you won't find it to be the aesthetic you're searching for, and that's fine.
Anyways. If you do decide to use Weatherwires, let me know and I'll be happy to provide any additional information.
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Topic: Need a Fort for a D&D Campaign (Read 883 times)