I have an abiding love of the megadungeon (defined here as a many-leveled dungeon large enough to be used as the centrepiece of a lengthy campaign), but I'm not always in the mood for one of the many variants of Dungeons & Dragons. Do any mega dungeons exist for systems other than one of the D&Ds?
I already know that I could make one, or convert any of the many D&D-system megadungeons and have fun with that in whatever system I like. What I want to know if there's already anything that is native to a non-D&D system or system-agnostic. Print-published, amateur online, or even out-of-print doesn't matter.