Underdark


 * This is an article on the Underdark setting. For the sourcebook, see Underdark (sourcebook).

The Underdark is the vast network of underground caverns and tunnels underneath the surface of Abeir-Toril. It is home to a host of evil beings driven deep into the caverns at the end of the age of demons.

Inhabitants
The Underdark is extremely dangerous, especially to those not native to it. There are the usual dangers associated with caverns: claustrophobia, occasional poor air circulation, and getting lost. There is no light except for occasional patches of fluorescent fungus; most Underdark inhabitants either have highly developed senses other than sight or have developed infravision. Food can be extremely difficult to find, and much of the natural vegetation is poisonous.

In addition to those dangers, the Underdark also is the home of many predators and often-hostile races, including Beholders, Derro, Drow, Duergar, Dwarves, Illithids, Kuo-toa and Svirfneblin.

Domains
The Underdark is not one giant cavern under Faerûn, but rather, many giant 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, seperate 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 varies from small subterrean fisures nigh impossible for adventures to crawl through to wide expanses of deep water that hide coral caves, hollowed out sections of ice in which creatures live, and places where fungus, bones, or even pure force form "caves".

This varied landscape is as dynamic as the surface of Abeir-Toril. Some areas are even everchanging over the course of time by underground magmarivers, the emptying of underground lakes due to cracks in the rock formed by earthquakes. Due to this fact maps of the Underdark are highly unreliable.

Environment
The Underdark's environment varies vastly from the surfaceworld, making adventuring through it a dangerous expedition. Just like trekking through a desert, adventurers traversing the Underdark's passages need to be well prepared.

The Underdark goes mainly without any source of light save for the occasional luminous rocks or funghi. Large portions of it go also devoid from food or water, making well stocked food supplies a must-have when exploring uncharted terrain underground.

Lack of light combined with a tomblike silence makes travelling something for the stronghearted. The nervewrecking silence makes even experienced adventurers grow aggitated after days full of it.

Just like deep dungeons, the air can grow stale and even poisonous in the Underdark. Add the possible existence of explosive gasses due to volcanic activity underground and deadly gasses bubbling out of deep fissures in the rock, and a warning doesn't seem so strange to all who wish to venture deep down below.

Bad air and poisonous fumes happen to collect in portions of tunnels and caves more or less isolated from the main vaults and caverns. Siphon-like tunnels holding water can also trap these gasses for a long time.

Climate
The temperature underground varies according to depth and the closeness of thermic activities in the area. Throught the year the temperate remains in most regions stable and moderate, usually on the clammy or chilly side. It's nothing a good warm cloak or warm furcoated leathers can't help to alleviate.

Venturing into the water underground needs a warning though, being never warmed by sunlight, it's freezing cold and known to cause death from hypothermia.

Ecology
Plant life and animal life can be as varried underground as on the surface. Ranging from small insects to hook horrors or Shadowdragons which have set up their realms deep down, everything can be expected. Plant life is unable to use sunlight as a source for energy, and thus takes on strange forms adapted to life underground. Many funghi are also found underground. Most of the time not being able to digest normal nutrients they rely on absorbing faerzress for their energy.