Underdark

The Underdark is an underground area in the world of Exandria on Critical Role, similar to the Underdark featured in many other RPG campaigns. A dark and hostile place, the Underdark is almost a world unto itself, with civilizations, monsters, politics, economies, and threats that are mostly separate from the surface world.

Environment
As a subterranean environment, the terrain of the Underdark is composed primarily of earth, stone, water (both still and running), and magma. Passages navigable by humanoids range from narrow tunnels to expansive caverns. Without sunlight, the Underdark exists in a perpetual night with the exception of the light from such sources as bioluminescence, enchanted hotstones, fire, and magma.

Moisture in many locations will condense on the walls and ceiling, and when it drips from the ceiling, the water droplets carry minerals and earth, which deposit on the dripping points from the ceiling and the landing points of the floor. Over time, these deposits form what are known as stalactites (hanging deposits, often shaped like downward-pointing spikes) and stalagmites (resting deposits, often shaped like spikes or conical mounds). From a combat perspective, stalactites may be broken free and allowed to fall as spikes, while stalagmites may offer cover or hiding spots if large enough. Both mineral formations may also hide dangerous denizens of the Underdark, ready to ambush unsuspecting creatures.

The Underdark may feature a wide variety of fungal growths and even mushroom forests.

Creatures
Most Underdark creatures either are blind (with no eyes or with vestigial eyes) or have excellent darkvision and/or infravision. Many creatures have other highly developed senses to compensate for the lack of sight, such as tremorsense or a keen sense of smell and/or hearing. During Vox Machina's travels in the Underdark, a series of rumbling noises kept occurring, and an illithid named Clarota advised them to keep still so as to avoid attracting unwanted attention through tremorsense.

Many creatures of different types live in the Underdark.

Humanoids

 * Drow (dark elves)
 * Duergar (gray dwarves)
 * See also: Category:Duergar.
 * Goblins
 * See also: Category:Goblins.
 * Kobolds
 * Svirfneblin (deep gnomes)

Aberrations

 * Aboleths
 * Cloakers
 * Illithid
 * Intellect devourers

Monstrosities

 * Basilisks - Kept by the duergar
 * Bulettes
 * Driders
 * Gricks
 * Ropers
 * Umber hulks

Giants

 * Fomorians
 * Ogres
 * Trolls

Fiends

 * Draegloths

Tal'Dorei

 * The Emberhold: A duergar stronghold accessible via the mines beneath Kraghammer. Came under K'Varn's control.
 * Yug'Voril: An ancient city lately controlled by an illithid colony that also fell under K'Varn's thrall. Even the illithid don't know who originally built it. Close to a rift with the Far Realm.
 * Ruhn-Shak: A small drow city beneath the Stormcrest Mountains, devoted to Lolth, the Spider Queen.

Wildemount
The Kryn Dynasty—particularly the Aurora Watch, with its magically controlled purple worms—largely controls the Underdark of continental Wildemount. They send assassins and spies, collectively called the Lens, through the Underdark to infiltrate other lands and seek out Luxon Beacons. Duergar hostile to the Kryn control perhaps a dozen small outposts. Deep gnomes also have some small settlements in the Underdark, and remain neutral between the Kryn and duergar.

Other Notable Locations
 * The Bastille of Torment, deep under the Dunrock Mountains, is presumably part of the Underdark. Torog used the Bastille to torture the enemies of the Betrayer Gods during the Age of Arcanum.
 * Fire giant citadel beneath the northern Ashkeeper Peaks
 * Miskath Pit: In Blightshore, a sinkhole of unknown depth that blends the Underdark with the Far Realm.
 * The Winding Core: A sliver of the Underdark on Rumblecusp.

History and Deities
Torog, the Crawling King, is the dark god of the endless tunnels and caverns beneath Exandria. His violent tears carved the pathways under the world.

The Calamity
One of the earliest casualties of the Calamity was Lolth, as Kord, the Storm Lord, impaled her with one throw of his thunderspear before her drow armies even did battle. At that point the drow were driven from the surface world and forced to rebuild their empire deep underground, where their nobility came under the influence of Tharizdun. Lolth's blood pooled in the dark caverns under the world, and her most loyal drow servants drank of the blood and became half-spider hybrids called driders. In Wildemount, some drow found the Luxon and took a different path.

When Torog was defeated, his violent tears burned tunnels into Exandria, and his followers fled into the tunnels. He was banished to a sliver of the Far Realm that now borders the deepest pits of the Underdark.