Ormash Sewers

Publisher's blurb:

Originally built to handle the rainwater and filth of the city, the ancient sewers have become a dark and dangerous refuge for unspeakable foulness. Deep channels of putrescent sludge flow through a twisting maze of coal-black tunnels, emptying into great pools before flowing into unexplored caverns or out to sea. This muddy muck is always moving, and conceals the most horrible of creatures under its opaque surface. The walls are fashioned with downspouts that periodically belch repulsive fluids into the mawkish ooze, making the precarious walkways and makeshift bridges even more slippery and dangerous.