The Underdark is an enormous system of subterranean caves, caverns, and tunnels located beneath the surface of Toril.
Mordekainen
Absence of light results in darkness. So, what results from the absence of Good? The Underdark is a place with very little of either.
Geography
- World Above: The name that those who lived in the Underdark gave the surface area of Toril.
- Upperdark: 4.8 kilometres below the surface. It was here where the surface dwellers and those in the Underdark most often met.
- Middledark: 4.8 to 16 kilometres below the surface, this layer was where most of the Underdark cities were located.
- Lowerdark: 16 kilometres or more below the surface, the Lowerdark was where even those who knew the Underdark were loath to go.
Domains
The Underdark is not one giant cavern under Faerûn, but rather many huge networks of caverns and caves. As a result, it is not always possible to travel from one end of the Underdark to the other. The Underdark is divided into several domains that are similar to continents of the world above. While it is possible to travel from one place to another within a domain, separate domains tend to have very few passages linking them. The major domains of the Underdark are the Buried Realms, the Darklands, the Deep Wastes, the Earthroot, the Glimmersea, Great Bhaerynden, the Northdark, and Old Shanatar.
Topography
The Underdark’s underground landscape vary from small subterranean fissures almost impossible for adventurers to crawl through to more conventional caves and caverns. But there are also wide expanses of deep water in which coral caves grow, blocks of ice that creatures hollow out and dwell inside, and cave-like spaces within masses of fungus, bone or else supported by bubbles of magical force.
This varied landscape is as dynamic as the surface of Toril. Some areas are always changing over time because of underground magma rivers or the emptying of underground lakes due to cracks in the rock formed by earthquakes. This means maps of the Underdark are highly unreliable.
Inhabitants
The Underdark is inhabited by many races, including aboleths, beholders, cloakers, derro, drow, duergar, dwarves, illithids, kuo-toa, quaggoths, rock gnomes, and deep gnomes.
Ecology
Plant life and animal life can be as varied underground as on the surface, ranging from small insects to hook horrors or shadow dragons, which set up their realms deep down. Anything can be expected. Plant life is unable to utilize sunlight as a source for energy, and thus takes on strange forms adapted to life underground. Many fungi are also found underground. Being unable to digest normal nutrients most of the time, they rely on absorbing faerzress for their energy.
Gallery
A map of the Underdark beneath western Faerûn