ShadowSea: The Stygian Depths (2011)

From the publisher:

Our group was not prepared for the horrors of the Stygian Depths, as we have named the accursed lands below. Naught else but the world of the damned did we find, with creatures that defied all laws of nature, adn where the very earth seemed to tear at our souls. THe catacombs penetrated deep below, twisting and turning until emerging into a nightmare city of demons, a place long forgotten by the civilizations of man an donly whispered of by decrepit sages searching through the crumbling ruins of the underlands. . .
Journal entry-Johan Kurtz, 1681

Expansion rules for the ShadowSea miniatures game allowing for dungeon crawls.