The Undermire was a network of ancient tunnels, chambers, and collapsed settlements buried beneath the Murkmire Marshlands, stretching through bedrock shaped long before Common Unification. It lay within the Upperways, a region of high subterranean passages that once supported trade, habitation, and ritual movement beneath the Fencrest Foothills; however, time, water, and neglect reduced it to a half-drowned ruin. Stone stairways ended in darkness, halls sheared away into flooded chasms, and entire districts lay entombed in silt and salt-preserved decay.
Much of the Undermire predated recorded history. Its earliest structures showed mixed workmanship, suggesting successive cultures built atop one another rather than a single founding people. Some scholars believed that during the Age of Giants, it functioned as a subterranean crossroads, linking inland routes to the Shifting Blue. When surface powers collapsed or shifted, the Undermire was abandoned, and its entrances gradually vanished beneath the marsh.
The Murkmire itself preserved the Undermire as much as it destroyed it. Saline bogs and slow-moving tides sealed lower reaches in airless water, preventing rot while eroding supports. Upper sections remained accessible but unstable, choked with mist, fungal growth, and drifting vapors that carried sound unpredictably. These conditions discouraged sustained exploration. Archaeologists from Cliffsunder recorded only fragments before being driven back by the terrain or creatures that lived within it.
Among the groups who utilized the Undermire were the Fold, who found its ocean connections and natural obscurity made it ideal for fencing. Using its covert networks, the Fold mapped viable routes through the Upperways and quietly redirected skilled labor into the depths. They reinforced or sealed entire sections, without leaving surface traces. Within this hidden infrastructure, the Undermire Dwarf-Door was constructed, anchoring a vault beneath the Murkmire Marshlands that housed the Fold’s treasury and sensitive records. The surrounding ruins masked both construction and access, and the Undermire’s reputation ensured few ever searched long enough to find it.