Ptolus: Beneath the Streets (3.5e)
As exciting as the surface of Ptolus can be¸ many adventurers find what goes on beneath the city streets to be of even greater interest. Most locals call such subterranean places collectively 'the Dungeon¸' and many adventures in the typical Ptolus Campaign take place below the city.
"Beneath the Streets introduces these areas¸ including Ghul's Labyrinth - a network of passages and rooms created long ago by a dark lord - and an 'unofficial' underground territory called the Undercity. Both adventurers and subterranean dwellers use the city's Sewers to get around underground. The book also covers Dwarvenhearth¸ an ancient city of treasure¸ guardians¸ and traps. And an extensive complex of natural Caverns below Ptolus holds its dread secrets¸ from dark elf fortresses to the lairs of the Galchutt's servants.