The Pit: Bunker of Unknown Origin

From publisher blurb:

Location: Jungles of Steel

Overview

The Pit is known to only a few, and even then is spoken of quietly and with an air of fear. But while the location of the Pit is a close kept secret, no one knows what lies at the bottom, and even those who have visited the strange bunker know nothing of its true origin. Rumours persist of some sickness or malaise haunts that the site, effecting those who spend too long within. Now a group or mercenaries have taken up residence in the upper levels and show signs of the sickness, and others are lost deeper in the bunker.