>>95957753
That's an old Castle Greyhawk layout, probably WotC-era (the vertical overview is definitely from Return to the Ruins of Greyhawk for 3e; I would think the level maps are too based on the tripartite layout, but I can't say with any certainty). In any case it's not authentic Gygaxian and definitely not from Castle Zagyg. The authentic level 1 of Gygax's Greyhawk Castle looks like pic related. The Castle Zagyg one looks different again.

Moreover, 2e is not an OSR game.