Underdark

The Underdark is a vast underground environment 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 may interact only sporadically or indirectly with the surface world. Notably, the Underdark has significant connections to the Far Realm, from which many aberrations emerge.

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. Natural cavern formations like stalagmites and stalactites abound; some predators camouflage themselves among them to ambush unsuspecting creatures.

Without sunlight, the Underdark exists in a perpetual night with the exception of the light from such sources as fire, bioluminescence, enchanted red glow stones, and magma. Without photosynthesizing plants, fungal growths and even mushroom forests are foundational for the food chain.

Creatures
Most Underdark creatures either are blind (with no eyes or with vestigial eyes) or have excellent darkvision. 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 Clarota advised them to keep still so as to avoid attracting unwanted attention through tremorsense.) Peruse the list below for examples.

Humanoids

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

Aberrations

 * Monster Manual 5e - Aboleth -p13.jpgths
 * Cloakers
 * Illithid
 * Intellect devourers

Monstrosities

 * Abyssal Abomination - Created by K'Varn
 * Basilisks - Kept by the duergar
 * Bulette feat.jpgtes
 * Driders
 * Gricks
 * Hook horrors
 * Purple worms - Kept by the drow
 * Ropers
 * Umber hulks

Giants

 * Fire giants
 * Fomorians
 * Ogres
 * Trolls

Fiends

 * Draegloths

Beasts

 * Bats
 * Small, sightless rats

Plants

 * Gas spores

Oozes

 * Black pudding

Undead

 * Ghouls

Tal'Dorei

 * Crystalfen Caverns: Deep beneath the Bladeshimmer Shoreline and even running beneath the ocean floor, the caverns were colonized before the Age of Arcanum by aboleths and other aberrations from the Far Realm. That civilization was gradually expanding toward the surface until it was literally crushed by forces unleashed in the final battle of the Calamity that tore through Exandria. Because of long exposure to psychic energies, the caverns have veins of azuremite, one of the substances that can be refined to make suude.
 * Episode-006-Emberhold-by-Son-of-Joxer.jpgEpisode-009-Yugvoril-by-Son-of-Joxer.jpgRuins of Salar: Salar, the Unseeable City, was the capital of the aberrations' civilization. Trysta excavates and studies the ruins.
 * The Emberhold: A duergar stronghold accessible via the mines beneath Kraghammer, after miles of walking. 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. Nearby there are veins of blue crystal matching the description of azuremite, but Vox Machina couldn't identify it at the time.
 * Vulkanon: The city-state, deep in the magma tunnels of the Cliffkeep Mountains, that serves as the center of fire giant civilization. Produces high-quality arms and occasionally allies with the duergar of the Emberhold.
 * 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 lava river - Anchuli Felicia King.jpgThe 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 untold depth that blends the Underdark with the Far Realm.
 * The Winding Core: A sliver of the Underdark on Rumblecusp.

Language
Undercommon is a trade language used by a variety of sapient Exandrian races of the Underdark. The duergar of the Emberhold, the drow of the Kryn Dynasty and Ruhn-Shak, and a Fomorian near Yug'Voril all speak Undercommon. Pike Trickfoot and her family of deep gnomes can speak Undercommon, though they only do so infrequently. The corrupted humanoid arcanists known as core spawn seers, interestingly, also speak Undercommon, as did the kuo-toa who served the beholder in Purvan Suul's sunken tomb.

Undercommon sounds reminiscent of the Tolkien universe's Black Speech: very guttural and deep.

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 discovered and drank of the blood, which transformed them into 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.

The final battle of the Calamity sent shockwaves through Exandria that caused mass collapses in the Underdark, crushing the civilization of aboleths and other aberrations that had occupied the Crystalfen Caverns.

Pre-Stream Adventures
Several members of Vox Machina fell into a trap that flushed them into a subterranean river system beneath Emon. They ended up in the Crystalfen Caverns, where they encountered an aboleth and then met Trysta in the Ruins of Salar. In exchange for eliminating an umber hulk who had recently settled nearby, Trysta told them how to exit back to the surface.

Chapter 1
Vox Machina delved from the Greyspine Mines of Kraghammer to the Underdark, with major stops in the Emberhold and Yug'Voril. They had been tasked with finding and extracting Lady Kima of Vord, but she insisted on taking down K'Varn, who had brought the duergar and illithid under his control and was threatening to expand upward.

Along the way, Vox Machina encountered a wide variety of creatures: monstrosities, aberrations, oozes, giants, and undead. They found a rift to the Far Realm near Yug'Voril.

While traveling through tunnels burrowed by the Kryn Dynasty's purple worms, the Mighty Nein skirted the top of the Underdark. There they encountered ropers, a kobold colony, and a pair of fire giants guarding entrances to a citadel.

Chapter 17
On Rumblecusp the Mighty Nein encountered a draegloth, which usually exists in the Underdark and was out of place in a tropical forest. Later, Vilya mentioned that the Winding Core on the island is like a sliver of the Underdark.