A One-Round Living Greyhawk Theocracy of the Pale Regional Adventure
From the introduction:
With the Demonic invasion turned aside, the now empty structures of Bitterhollow seems to have attracted a few squatters. Several small squads have been tasked to investigate, and with armed forces still running thin – an old acquaintance request for your expertise in some underground matters.
A subterranean epic for [player characters] who aren’t afraid of the dark; [levels] 2 - 10.