The Darklands is the collective term used to refer to the innumerable systems of caves and caverns that can be found across the world. The boundary between an ordinary cave or tunnel and those of the Darklands is highly indistinct. The Darklands ranges from easily accessible subsurface chambers to highly remote caverns miles underground; the farther underground one ventures, the more unusual and hostile the Darklands become. Most of the Darklands remains poorly mapped and little understood to the surface world.
Inhabitants of the Darklands vary greatly. Strange, otherworldly creatures can be found in the depths, many highly unlike anything on the surface. Individuals of many ancestries live in the Darklands, including drow, duergar, dwarves, xulgaths, deros, and a great deal more. Partially in response to the ever-hostile conditions in which they live, many Darklands denizens harbor a strong dislike of outsiders. Peaceful communities exist, but they are exceptions to the rule, and travel underground away from the Low Road can be very hazardous. Some large cities have grown in the Darklands, but most settlements remain small and isolated.
Strange phenomena can occur far underground. The Darklands warps are one of the most notable of these, rifts in otherwise unremarkable passages that can distort space and distance.