Whizbang Dustyboots
Gnometown Hero
Castle Zagyg is Castle Greyhawk and its dungeons with the numbers filed off, reconstructed from Gygax's notes and memories. It's not exact, in part because the old dungeon was a constant work in progress and this is just a snapshot, but also because Gygax in the early 2000s was a different person than he was in 1974.So the Castle Zagyg book is a megadungeon akin to Castle Greyhawk?
Edit: I think I see that its a campaign setting only.
It was never completely published when EGG died and the Troll Lords had to stop selling it due to rights issues.
Yggsburgh is the setting that goes around the castle. If I remember correctly, there are plenty of adventure sites in it, even without the castle proper. And, as I recall, the actual Zagyg setting started with more upper level ruins/surface releases than you'd expect. But again, that means there's lots to do even before one gets fully into the dungeon.