This is my response to a mega-dungeons thread over on RPG.net, so it may offer some other suggestions, Reynard: all of them will require conversion of one form or another, though.
Also: if you're looking for premade maps, there are many you can use, too:
- 0one's
Dungeons Under the Mountain
- Rob Kuntz's and Ramsey Dow's
Dungeon Sets
-
Ramsey Dow's Sickly Purple Death Ray blog
- the various posters sharing levels in threads on
Dragonsfoot and
Knights & Knaves Alehouse
===
For folks not interested in reading the thread @ rpg.net, I posted this reply there, with a summary of mega-dungeon products currently available, published in the past, or interesting ones forthcoming soon-ish. I was really surprised at the sheer volume of mega-dungeon material published to date (the list took a half-hour to compile or so, so it wasn't quite the quick reply I was planning to write...):
For 0e/1e, I recommend folks check out the following mega-dungeons, in roughly this order:
- Castle Greyhawk, in various incarnations (going backward from newest to oldest): Castle Zagyg from TLG*; Expedition to Ruins of Greyhawk from WotC; Greyhawk Ruins from TSR; WG7 Castle Greyhawk from TSR [generally ignored]; extracted levels from the original castle of Gygax and Kuntz, including EX1 Dungeonland (1983), EX2 Land Beyond the Magic Mirror (1983), and WG6 Isle of the Ape (1985) by EGG---and three by RJK: Garden of the PlantMaster (1987, 2003), “The Living Room” (2007) and Bottle City (2008); Black Blade will publish Kuntz's Machine Level from the original castle when Rob completes it
- Maure Castle and Castle El Raja Key (by Rob Kuntz, in Dungeon magazines 112, 124, 139, and with free levels published in The Oerth Journal and on the now-discontinued Pied Piper Publishing site; TSR module 1e WG5 Mordenkainen's Fantastic Adventure also ties into Maure Castle)
- Caverns of Thracia (Judges Guild and Necromancer Games for d20 expanded version): Paul Jaquays' original from Judges Guild was expanded upon by NG, and both are worth digging up if you're interested in running it; Caverns of Thracia is probably still the single best mega-dungeon that's been published as a final/finished product
- Tomb of Abysthor (Necromancer Games d20): this is the best module Necromcaner ever published, and is comparable to Caverns of Thracai in size/scope)
- Phil Barker's Jakállan Underworld (Empire of the Petal Throne/Tekumel mega-dungeon; forthcoming)
- Dungeons of Castle Blackmoor (JG First Fantasy Campaign): I'd ignore the 20 level version from Zeigteist Games---Dungeons of Castle Blackmoor (2006)---since the last 10 levels are clearly added filler, and are completely out of style with the first 10 that Arneson actually designed
- Ruins of Undermountain (Ed Greenwood's Forgotten Realms mega-dungeon): 2 boxed sets, 3 separate modules, and some Dungeon adventures too; the first boxed set is the meat in this offering, but much like Castle Greyhawk, you get a better sense and flavor of the original version from reading Greenwood's articles in The Dragon, prior to the publication of the FR boxed set in 1987
- Rappan Athuk (Necromancer Games d20): you'll have to re-convert the content back to 1e, and while in general RA's levels are too small to constitute a real mega-dungeon, they are useful as sub-levels or just for general inspiration/ripping off good encounters
Several OSR publishers/writers/bloggers are working up mega-dungeons, too (in alphabetical order; I'm probably forgetting some others already published/available, and if so, do chime in with them!):
- Anomalous Subsurface Environment (Patrick Wetmore's the first level of his science-fantasy mega-dungeon)
- Castle of the Mad Archmage (Joe Bloch's mega-dungeon, steeped in the traditions and inspirations of Castle Greyhawk; available at his Greyhawk Grognard blog, and forthcoming from Black Blade)
- Dwimmermount (forthcoming from James Maliszewski, of Grognardia fame)
- Fight On! magazine's in-house megadungeon, The Darkness Beneath (published serially in FO!)
- The Rogue Games Dojo (seemingly on hiatus, but it was a freely available mega-dungeon with OSR fan submissions as well as some encounters/levels by James Maliszewski and other OSR notables)
- Stonehell by Michael Curtis, of The Society of the Torch, Pole and Rope fame (Volume 1 covers levels 1-6, with Volume 2 in the works)
Other titles you may find worthwhile, but which I don't have any experience with (also listed in alphabetical order):
- Castle Whiterock (Goodman Games, d20)
- DungeonADay.com (Monte Cook's project, seemingly just getting over some DNS issues/technical hosting difficulties)
- Rod of Seven Parts (TSR, 2e; the dwarven citadel maps were also extracted by WotC and published as a Map a Week project sometime in the 3.0 era)
- World's Largest Dungeon (I really can't stomach this product at all, but several folks have commented that it's worth getting for the maps)
* I wrote a long review of Castle Zagyg, which touches on many aspects of good mega-dungeon design as part of the analysis of that product; if you're curious, it's @
http://www.greyhawkonline.com/grodog/gh_grodog_castle_zagyg_review_final.pdf