When it comes to published megadungeons, nothing comes close in size or scope to Halls of Ardun Vul. I actually own Arden Vul in print, which is a many-volume hardcover set. I have yet to give it the complete reading it deserves.
Halls of Ardun Vul is a current offering on Bundle of Holding. Normally $109, and currently on sale for $81.75 in PDF, you can get Halls of Ardun Vul for $24.95 via Bundle of Holding. At that price, every old-school gamer should own a copy.
Arden Vul is the most ambitious megadungeon ever created, with over 1,100 Pages of Incredible Adventure. This First Edition compatible fully-bookmarked PDF product features:
- 2,162 Encounter Descriptions
- 14 NPC Factions
- 10 Massive Levels
- 15 Extensive Sub-levels
- 7 Dangerous Exterior locations
- 149 New Monsters
- 332 New Magic Items
- 69 New Technological Items
- 44 New Spells
- 189 New Books through which PCs can gain a deep understanding of the dungeon
- A full NPC appendix with 10 competing parties at 3 levels of power
- Over 140 original pieces of art, including 28 full-page illustrations!