Underdark

The **Underdark** was the enormous system of subterranean caves, caverns, and tunnels located beneath the surface of Aegirrim

## Geography

* World Above: The name that those who lived in the Underdark gave the surface area of Aegirrim.
* Upperdark: The first 3 miles (4.8 kilometers) below the surface. It was here where the surface dwellers and those in the Underdark most often met.
* Middledark: Located 3​ to ​10 miles (4.8​ to ​16 kilometers) below the surface, this layer was where most of the Underdark cities were located.
* Lowerdark: 10 miles (16 kilometers) or more below the surface, the Lowerdark was where even those who knew the Underdark were loath to go.

### Domains

The Underdark was not one giant cavern under Aegirrim, but rather many huge networks of caverns and caves. As a result, it was not always possible to travel from one end of the Underdark to the other. The Underdark was divided into several domains that were similar to continents of the world above. While it was possible to travel from one place to another within a domain, separate domains tended to have very few passages linking them. The major domains of the Underdark were:

* Buried Realms
* The Darklands
* The Deep Wastes
* The Earthroot
* The Glimmersea
* Great Bhaerynden
* The Northdark
* Old Shanatar
* The Underrot

## Topography

The Underdark's underground landscape varied from small subterranean fissures almost impossible for adventurers to crawl through to more conventional caves and caverns. But there were also wide expanses of deep water in which coral caves grew, blocks of ice that creatures hollowed out and dwelled inside, and cave-like spaces within masses of fungus or bone or else supported by bubbles of magical force.

This varied landscape was as dynamic as the surface of Aegirrim. Some areas were 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 meant maps of the Underdark were highly unreliable.

### Maztica

The Underdark burrowed deep under the Shimmering Sea, stretching between the continents of Elodria and Yveria. Ancient dwarven legend talked about a great ancient war between the stout folk and the drow that raged in the depths underneath the Shimmering Sea. The war was ended by drow magics that lit the tunnels with fires so hot they melted rock and flooded the portion of the Underdark that connected dwarves and drow who resided in the Yverian Underdark with their western kin. In fact, the catastrophe was known as Rockfire and took many dwarven generations before the "discovery" of Yveria by duergar explorers. The calamity was caused by uncontrolled magics of the *Darkfyre* harnessed by the drow. It left Underdark beneath Yveria believed to be uninhabitable, filled with poisonous gas and molten rock. The dwarves who became cut off from Elodria, with passing centuries became desert dwarves who lived in shallow caves close to the surface of the Daqha desert. They believed that the Rockfire completely exterminated the drow and the rest of the dwarves. However, that was proven to be a false belief by the Third Era. The Underdark passages between the two continents were believed to be lost legends, gone, and forgotten by inhabitants of Elodria.

## Environment

The Underdark's environment varied vastly from the surface world, making adventuring through it a dangerous expedition. Just like trekking through a desert, adventurers traversing the Underdark's passages needed to be well prepared.

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

Lack of light combined with a tomb-like silence made traveling something only for the strong-hearted. The nerve-wracking silence made even experienced adventurers grow agitated.

Just like deep dungeons, the air could grow stale and even poisonous in the Underdark. It could contain explosive gases from underground volcanic activity or other deadly gases bubbling out of deep fissures in the rock. Bad air and poisonous fumes could collect in portions of tunnels and caves more or less isolated from the main vaults and caverns. Siphon-like tunnels holding water could also trap these gases for a long time.

## Climate

The temperature underground varied according to depth and the proximity of thermal activities in the area. Throughout the year, the temperature remained stable and moderate in most regions, usually slightly clammy or chilly. The water underground was extremely cold and posed a hypothermia risk.

## Inhabitants

The Underdark was inhabited by many races, including aboleths, beholders, cloakers, derro, drow, duergar, dwarves,illithids, kuo-toa, quaggoths, rock gnomes, svirfneblin,

## Ecology

Plant life and animal life could 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. Plant life was unable to utilize sunlight as a source for energy, and thus took on strange forms adapted to life underground. Many fungi were also found underground. Being unable to digest normal nutrients most of the time, they relied on absorbing *faerzress* for their energy.

Some dangerous flora of the Underdark were the exploding bibberbangs.