From the back of the book:
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.
This is one in a series of nine Ptolus PDF releases from Malhavoc Press. When used together, they comprise the entirety of the Ptolus print book.
Each one is also usable on its own for city-based fantasy d20 roleplaying campaigns.