The Underdark
Government City-states, others
Population Unknown
Races Aboleth, cloaker, drow, duergar, illithid, quaggoth, svirfneblin
Religions Drow pantheon, Deep Duerra, others
Alignment Mostly evil

The Underdark is the vast network of underground caverns and tunnels underneath the surface of Toril.

Levels[edit | edit source]

World Above
The surface area of Toril. The name those who live in the Underdark give the surface.
Upperdark
The first three miles below the surface. It is here where the surface dwellers and those in the Underdark most often meet.
Middledark
Located three to ten miles below the surface, this layer is where most of the Underdark cities are located.
Lowerdark
Ten miles or more below the surface, the Lowerdark is where even those who know the Underdark loath to go.

Inhabitants[edit | edit source]

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 darkvision. 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[edit | edit source]

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.

Other Domain Sites and Cities[edit | edit source]

  • Oghrann[ Upperdark of the Plains of Tun ]
  • Sshamath, the City of Dark WeavingsMetropolis, Drow; Middledark)

[ Beneath the Far Hills ]

  • Throrgar, the Shrieking Abyss[ Lowerdark of Chionthar ]

Biodomes[edit | edit source]

Topography[edit | edit source]

The Underdark's underground landscape varies from small subterranean fissures almost 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 magma rivers or the emptying of underground lakes due to cracks in the rock formed by earthquakes. This means maps of the Underdark are highly unreliable.

Environment[edit | edit source]

The Underdark's environment varies vastly from the surface world, 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 fungi. Large portions of it are also without from 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 makes travelling something for the strong-hearted. The nerve-wracking silence makes even experienced adventurers grow agitated after a few days.

Just like deep dungeons, the air can grow stale and even poisonous in the Underdark. It can contain explosive gases from underground volcanic activity or other deadly gases bubbling out of deep fissures in the rock. Bad air and poisonous fumes can 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 gases for a long time.

Climate[edit | edit source]

The temperature underground varies according to depth and the proximity of thermic activities in the area. Throughout the year the temperature remains stable and moderate in most regions, usually slightly clammy or chilly. The water underground is extremely cold and poses a hypothermia risk.

Ecology[edit | edit source]

Plant life and animal life can be as varied 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 fungi are also found underground. Being unable to digest normal nutrients most of the time, they rely on absorbing faerzress for their energy.


The Duergahydra went first, sometime around the year 50 DR, and the Mornhound died out far more recently (in the 1100s).

The Duergahydra, or 'gray evil of the Underdark,' was a smaller subspecies of the hydra. Possessed of a hard, gray stony hide and darkvision, it was an omnivorous, agile climbing and clinging lizard of long, whiplike build (long neck, long tail, central body about the size of a tall human) and swift, darting movement. All duergahydra were born with two necks and heads, and customarily kept one in reserve, bent around and hidden on their backs so as to resemble a hump or folded wings. However, if a duergahydra head or neck was damaged or severed, two grew in its place (unless the same preventative means as prevent trolls from regenerating were applied), from the stump or shrivelling and drying ruin of the original. In this way, an aggressive duergahydra could end up with six, seven, or more heads, becoming larger and slower with each one (until some became too massive to move at more than a painful crawl, and starved to death, losing their regenerative abilities with their lives). Duergahydra instinctively 'knew' they could heal, and were apt to be bold and aggressive in their hunting, literally sticking their necks into danger often. They were cunning, and quickly learned the details and tactics of prey and foes. Duergahydra always hunted alone, pairing only briefly (a matter of hours) to mate, and were fiercely independent. When they proved untrainable as mounts or guardians, and impossible to 'cow' or threaten into keeping away from human settlements or valuables, humans started slaughtering them on sight -- and eventually succeeded in eradicating them (unless some cunning mage kept eggs or live specimens in some sort of magical stasis).

Their ichor was useful in healing and regenerative potions known to the drow and illithids, who'd hunted them to near-extinction long before humans became widely aware of their existence.

Mornhounds, on the other hand, were all too useful, and eventually perished because of that. Resembling large, shaggy Irish wolfhounds, they would in 3.5e terms be very close to a dire wolf -- except that they were easily domesticated (to be steeds as well as hunters and sheep-herding experts usually able to operate without their human trainers), VERY loyal and very intelligent (able to carry messages and deliver them according to the situations they found, e.g. "give this scroll to Baeruld, but not if he's a captive or Dunthlass is also present").

In the wild, packs of mornhounds roamed the Heartlands and the Sword Coast North about as far north as the Evermoors, but many creatures (from orcs to dragons) found their flesh tasty and devoured them with enthusiasm, until they faded into the deepest woods, dwindling down to a few companions to human druids and wood elves... and eventually, oblivion.

Souses[edit | edit source]

The thing that's really missing in most places underground is a source of energy to drive the ecosystem. Here are some possibilities for things that could form the basis of the ecosystem:

  • Organotrophic organisms utilizing detritus from the surface as an energy source. This is how most cave ecosystems survive today. Animals, groundwater, and streams bring biological material into the cave, which is used as nutrition by fungi and other animals as the basis for an ecosystem.
  • Chemotrophic organisms using chemical energy from volcanic gasses or other sources. This actually powers some extreme ecosystems on Earth. Hydrogen Sulfide from volcanic eruptions can be used by certain bacteria as an energy source, and this supports a very complex ecosystem in deep-sea Black Smoker environments.
  • Lithotrophic organisms the utilize the minerals in the rocks around them as an energy source. If they got to be effective enough, they could be the basis for an ecosystem, and carve out huge caverns underground. Lithotrophs actually exist, but are not known to support large ecosystems or create huge caverns.
  • Geothermal energy could also be a possiblity, if a life-form evolved that can exploit a geothermal heat gradient to grow. Other life forms would exploit the geothermal creatures to survive. This is possible, but probably very unlikely. An underground civilization is much more likely to utilize this as a secondary power source similar to the way we use oil.

Trade[edit | edit source]

Underdark river freight traffic goes on "snakes" and "skimmers." A snake is a series of log-like hollowed-out giant Underdark beetle carapaces, joined end to end by giant-spiderweb ropes to form a flexible sequence of cylinders that hold cargo (like a toy snake made of wooden cylinders joined end to end). They are paddled and poled by "steerers" at the head end - - and if they're long, the middle, too - - a dangerous job if the river runs fast. A skimmer is like a kayak (long and narrow), but has a wider deck atop it that supports hinged "rise and fall" outrigger pods made of insect chitin (bodies of large beetles, sealed to be made watertight), that can spread out where the watercourse is wide or be folded over top of the deck where it gets narrow. Cargo goes in the kayak body under the deck, and atop the deck (shrouded against wet), not in the pods, which are for flotation only.

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