The Undermarket is "an otherworldly bazaar offering all manner of goods and services, all temptations a man could imagine and several he couldn’t. Anything can be purchased there if one is willing to meet the price, which is rarely monetary; blood, firstborns, and souls (yours or someone else’s) are all accepted forms of currency." It is accessible both in Countermay, where the Merchants of Esh initially set themselves as intermediaries between mortals and the demonic Marketeers, and Fartherall, where access to the Undermarket has caused wars.
- The arcanoquake from Ulix's attempt to tap into a Nexus tore a hole between worlds and exposed the Undermarket. "Since the discovery of the Undermarket, Esh has ballooned into a sprawling mercantile metropolis ruled by an oligarchy of trade princes—men most able or willing to barter with the entities in the Undermarket."
- After the Denizaal conquered Countermay's Veil world, the Pex sold legal rights to that realm to the Undermarketeers in exchange for passage to a new world, which is how they ended up under The Shadow's abandoned Dracospine fortress in Fartherall.
- On their way through the Undermarket, the Pex stole certain treasures they later used to barter respect in Fartherall, along with advanced arcanophagic weapons and firearms used to force the human and dwarf forces out of the Dracospine fortress. The Pex maintained a monopoly on Undermarket connections in Fartherall, and their access to arcanophagic weaponry would later define their place in Fartherall and lead to the spark that began the Centuries War between the United Powers and the Free Nations Mutual Defense Pact.
- Denizaal warriors were often hired as mercenaries through the Undermarket.
- Cedric Humm, a human bard from Countermay, was a terrible kazooist who arrived in Fartherall after getting lost in—and later expelled from—the Undermarket.
- The Undermarketeers left Fartherall in 1746, when the Dream Bells shattered following the removal of the Godsword Aion from the tomb of Yir, the First God, located on the moon.
- As part of the Lonely Tower Accord that ended the Centuries War, the United Powers required the Pex seal the cleft to the Undermarket below the Pex capitol Prosperity and return the land to the dwarves. The dwarves, not knowing the connection to the Undermarket was long gone, had hoped to gain ties to the Marketeers and were furious at the alleged deception, but the Pex won in court.
- Around the year 1901 (the beginning of Underking Lum's rule and the founding of the Dwarven Imperium), the dwarves uncovered the Undermarket again, deep in the mountain.
- The Dwarven Imperium dropped an archanophagic city-killing bomb (CKB) bought from the Undermarket on the Rimic capital Cryopolis.
- Vancil, Matt, and Nathan Rice. Romance of the Nine Empires: Rules of Play. Edited by Jeff Quick, Alderac Entertainment Group, 2013.
- Vancil, Matt. The Fartherall Companion. Edited by Awen Inisfail Rowan-Nelson, Zombie Orpheus Entertainment, 2020.