Colloquially known as "The Ditch," the network of underground passageways and crevasses called the Erdwal originated as trenches created by Nephalians in each of the major cities of Havengul, Drunau, and Selhoff for resisting zombie and werewolf attacks. Over the years, the trenches between the three cities were connected into a network of defensible walkways for transporting goods and continuing trade even while wandering zombie hordes, demonic fiends, hungry geists, or the Krallenhorde wander about looking for victims. Major merchants of Nephalia have paid special attention to the uses of the Erdwal and have put serious resources into making it a legitimate artery of trade, thus it has developed a bustling underground economy of its own dealing in all manner of grey- and black-market goods: human blood, assassinations, counterfeit silver, necromancy, curses, and bloodsport.

Near the larger towns, the Erdwal becomes a trench marketplace of colorful rogues, seedy merchants, filthy sailors and gaunt strangers, all doing business in dark alleyways and roughly hewn tunnels branching off the main trench. Along the clandestine nooks, the skaberen and ghoulcallers ply their trade and human blood is bought and sold by the flagon. Flesh golems are created and experiments in transmuting base metals into pure silver are carried out. Skaberen stitch together hideous monstrosities, some of which get loose and cause havoc throughout the Ditch. As long as these dark dealings do not make it above ground level, the Church of Avacyn and its cathars do not intervene. Nephalia is a province of "understandings," and this is one of those uneasy truces that, if maintained, benefits all parties concerned.

Savage vampires lurk in the Erdwal's network of passageways where prey is plentiful and easy to catch.