Of all the tropes of fantasy, the Underdark of Dungeons & Dragons campaign setting Forgotten Realms is probably one of my favorites. It is a concept I often borrow for my own world building.
My own, loosly defined, fantasy world has an extensive underdark filled with both wonder and horror – a world beneath the world, usually referred to as “The Underside”. While large parts of the Underside is a pitch black, mostly lifeless labyrinthine wasteland, there exists also beacons of life and (to some degree) civilization. It is a vast, dark cosmos in which subterranean societies thrive beneath the feet of an unsuspecting world.
To the people of the above, this place is alien and terrifying and very dangerous.
The underside of the world has it’s own sprawling network of connections, much like the roads of the “surface”. Tunnels stretch for thousands of miles, and are used for trade and travel between the different creatures and settlements of the inky blackness.
One such “road” is the endless tunnels of the Stygian Trail, and to use it means paying tribute to whoever currently occupies the ancient toll houses. It is contested territory – bitter wars and countless skirmishes has been fought over the Stygian Trail and its fortified tollhouses. This map shows one of those toll houses, with enough room to house a small band of humanoid guards and plenty of storage for tribute.
Getting past the small fortress will not be cheap, and the toll master might not settle with gold coins – there are more valuable resources in the dark.
Oh, and if I’ve inspired you to run underdark adventures of your own, make sure you pick up a copy of Veins of the Earth by Patrick Stuart – it’s by far the best module I’ve ever read on the subject!