It is common knowledge that Dwarves and other folk of the Underworld make use of mine carts and tracks to move raw materials from one area to another. Less known to surface dwellers is the existence of an extensive railway system that connects disparate subterranean enclaves and strongholds. Tracks and tunnels can extend for many leagues, crossing under seas and monolithic mountain ranges. A minority of railways are well-maintained and trafficked by the slave-engines* of the Grey Dwarves. Many others have fallen into disrepair for various reasons: populations have receded to other zones of the Underworld; troglodytic monsters have made certain regions impassible; flooding or lava-upflow has made travel impractical and difficult. So-called "complete" maps of the Railways are invariably cheap knock-offs of the invaluable Dwarven originals and contain many errors and outright fabrications.
*Slave-engine: The rail-equivalent of a sea-going galley. Slaves are often seated in pairs and operate leg-driven wheel systems. Moderate-sized engines are pulled by thirty slaves or more. Slave-engines are often used in large-scale mining operations but are not limited to this area. Wealthy dwarves have teams of slaves to pull their private carriages and house-cars.