Sewers of Oblivion

From the back cover: "This solitaire takes place beneath the City of Terrors, but is not directly connected with that solitaire adventure. Sewers of Oblivion is not for novice adventurers - instead characters up to 7th level, with as many as 425 combat adds, will find a challenge or two within. However, less mighty characters (150-300 combat adds) will find a more exciting adventure and greater rewards in the end."