Underdark

The Underdark is a vast subterranean realm inhabited by drow, mind flayers, aboleth, and other strange, sinister creatures. It is comprised of three layers, known as the Upperdark (the first 3 miles beneath the World Above), the Middledark (3 to 10 miles below the surface), and the Lowerdark (10 miles or deeper).
The Underdark is not one giant cavern under Ekaia, but rather, many huge networks of caverns and caves. It is a place where few humans go and from where even fewer return. When entrances are found, they are far more often than not quickly covered up, either by the fearful surface dwellers who discovered them, or by unknown creatures below who do not wish their homes to be accessible.
Undercommon is the language spoken by the vast majority of denizens of the Underdark. Currency is not used by many races, but more civilized races such as drow and duergar use small, thick gold and silver coins with their own symbols carved into them, called malad by the drow and gishna by the duergar.

Settlements

The different communities of the Underdark are in some ways comparable to islands, separated by stone rather than water. Most large cities are located in enormous caverns, while smaller settlements are in sprawling cave systems, though there are many exceptions to this trend. The vast majority of settlements located in the Upperdark have hidden points of access to the World Above. A common way of linking different communities in separate cave systems is via teleportation circles; many, many magic users make a business out of this, charging a certain fee to cast this spell for clients to send them to various locations in the Underdark.
The largest cities in the Underdark, all drow cities, are Turaz-Gul, Undolath, and Stellmere. These names have been heard and found by scholars of the Underdark who reside on the surface, but their locations have never been ascertained. Smaller settlements whose names have been heard but whose existence has not been verified include Hoelenbrek (duergar), Ramivris (drow), and Endesfadell (svirfneblin).

Religions

Deities such as Synékia, Illethar, Dzuzce, Lomé, and other evil-aligned gods and monsters are revered and even worshiped commonly throughout the Underdark.

Interactions with Surface World

It is widely assumed that most excursions by Underdark denizens to the surface world occur covertly, and therefore cannot be accounted for. Generally civilized races of the Underdark venture to the world above to steal resources or people, and descend again as quickly and discreetly as possible. A common fear, and justifiably so, is being kidnapped to be sold into slavery, behavior documented by drow, duergar, and illithids. It is estimated that fewer than 0.2% of surface dwellers stolen away by Underdark denizens for any reason are ever heard from again.

Type

Cave System

Included Locations

• Turaz-Gul