An Underdark Primer
While many surface dwellers, regard the Underdark as all the same (one big cave, infested with hungry monsters), the wise adventurer prepares by studying what surface dwellers know about the Realms Below before venturing underground. Knowing what sorts of creatures and dangers lurk at what depths might mean the difference between life and death.
The Underdark is divided into three general levels: The Upperdark, the Middledark, and the Lowerdark.
The Upperdark extends from the surface to a depth of about 3 miles. Varied races inhabit this region,, including chitines, drow, dwarves, giants, all manner of goblinoids, orcs, svirfneblin, and wererats. Scouts from deeper races often venture into the Upperdark in order to trade with (or prey on) the races native to this area.
The Upperdark's main import from the surface is slaves. Slavers from evil-aligned cities in the Upperdark make frequent forays into the light to capture new slaves for use as either labor or food. They also trade for textiles, grains, fruit, and weapons. Their exports include raw ore, refined metals, gems, and native Underdark plants.
Travel in the Upperdark is relatively easy. Multiple paths to a single point usually exist, thanks to millennia of natural processes, volcanic activity, burrowing creatures, and various races cutting trails through the rock. In most places the surrounding earth is composed of rock, but near the surface, tunnels can be hewn out of tightly packed dirt, allowing creatures with burrow speeds that can't cut through rock to blaze their own trails in a pinch.
Surviving in the Upperdark
Survival checks made to hunt, forage, and avoid natural hazards in the Upperdark use the same DCs as normal surface conditions. Basic amenities such as light, air, food, and water are less available in the Upperdark than on the surface, but they are common enough.
Luminescent flora and faerzress provide occasional light; though not consistently enough to allow a creature without darkvision to travel without an independent light source. Vents from the surface keep air fresh and moving in the passages, so air quality is rarely an issue. Enormous underground lakes spread across hundreds of miles in some regions, and water trickles down from the surface in many others. Many water sources are guarded or fouled, but quite a few are both clean and open for anyone to use. Many different types of wild fungi are edible, and the Underdark equivalent of small game (rats, dire rats, lizards, and giant vermin) can easily be found in the tunnels. Domesticated animals, such as deep rothé, can also be found near most major population centers.
Denizens of the Upperdark
Most Upperdark inhabitants traffic with the surface world in some Way, either trading with or raiding their upstairs neighbors for things they can't get in their native habitat. They also trade with (and raid) each other. No Underdark community is ever really friendly with another, but Upperdark settlements often observe wary truces with their neighbors.
Chitines: Though they are sometimes considered too small, weak, or fearful to matter, chitines are quite capable of killing those who underestimate them. They are far more clever and malicious than they seem to be - clever enough to avoid fights they're not sure they can win, at the very least. Chitine nests can be found in web-filled caverns throughout the Upperdark, but the largest concentration of these spiderfolk is the realm of Yathchol in the northern Underdark.
Dwarves: For thousands of years, the great dwarven realms of the surface world have expanded downward instead of outward. Neither gold dwarves nor shield dwarves harbor any fear of the Underdark, and their cities are often buried in the upper reaches of the Realms Below. The kingdom of Iltkazar is the strongest shield dwarf realm remaining in the Underdark, and the gold dwarves there retain extensive Underdark holdings in the vicinity of the Great Rift.
Unlike the duergar, who prefer the deeper portions of the Underdark, gold and shield dwarves keep fields and livestock on the surface and trade extensively with surface folk. These dwarves are gifted engineers and industrious workers, and they have built many roads and bridges in the Underdark.
Goblins: Bugbears, goblins, and hobgoblins often establish outposts and settlements in the Upperdark, from which they can easily raid nearby surface lands. Goblinoids may in fact be the most numerous of the Underdark's races, but they have raised no great cities and delved no great caverns. Most goblinoid tribes exist in a state of barbaric squalor. Goblins in particular are commonly found as slaves in the cities of crueler and more sophisticated races, such as the drow and the duergar.
Quaggoths: These so-called deepbears frequently band together. to raid and forage throughout the Underdark. They once had a kingdom, Ursadunthar, deep beneath the Spine of the World, but it fell to the duergar of Gracklstugh in -1350 DR. Most quaggoth bands now survive by roaming the deeps as nomadic hunter-gatherers and supplementing their diets with anything (or anyone) that falls into their bloody claws. Like goblins, quaggoths are frequently encountered as slaves in the cities of more civilized Underdark denizens, such as drow.
Minotaurs: Hulking and fierce minotaurs dwell in the Upperdark, usually favoring the most confusing and complex cave systems for their lairs. Minotaurs generally live by raiding and plunder, although more than a few sell their services to other folk who offer gold and food in exchange for a chance to fight. Minotaurs are kept as slaves by Upperdark dwellers such as drow and mind flayers, but such slaves are not numerous.
The vast delve known as the Labyrinth was once a minotaur empire of sorts. While no signs of the former minotaur civilization remain, thousands of the creatures still infest the area.
Orcs: Like goblins, orcs often settle in the upper caverns of the Underdark. Caverns close to the surface offer shelter from the hated sun and easy defensibility with a minimum of work, and most orcs are only too happy to take advantage of that combination. Orcs are often enslaved by deeper-dwelling races, so they can be found almost anywhere in the Underdark.
Svirfneblin: The deep gnomes live in hidden caves and secretive strongholds throughout all three layers of the Underdark, but most of them dwell in the Upperdark and Middledark. Deep gnomes avoid trouble by simply staying well clear of it, and few strangers ever blunder across svirfneblin towns.
The svirfneblin city of Blingdenstone fell recently to a demon-spawned drow assault.
Stone Giants: Powerful and ponderous in action and thought, stone giants are strong enough to keep all but the most magically powerful of foes at bay. These creatures delve enormous quarries for their homes, and they can work wonders with their chosen medium.
Few in number, stone giants leave other folk alone and expect the same courtesy from anyone passing through their lands. The most powerful stone giant realm is the kingdom of Cairnheim, beneath the Giant's Run Mountains.
Troglodytes: Perhaps no other race is as universally detested as the troglodytes. These bloodthirsty savages descend on the realms of other Underdark folk like a plague of locusts and immediately set about raiding, pillaging, and killing anyone unfortunate enough to be nearby. They occasionally serve as slaves to more powerful races, but only in those places where more tractable (and less vile) slaves aren't widely available.
Troglodytes were once much more widespread in the Underdark than they are now, but they have been rooted out and exterminated in many places. Most troglodytes now live in the southern portions of the Underdark, particularly beneath the Mhair and Black Jungles.
The Middledark lies between 3 and 10 miles beneath the surface of Faerûn. Most larger cities of drow and duergar are in the Middledark. Other inhabitants include lone aboleths, cloakers, derro, grimlocks, and kuo-toas. A few mind flayer outposts are scattered throughout this level as well.
Settled communities in the Middledark commonly send trade caravans and raiding parties to the surface, or at least up to Upperdark trading centers such as Menzoberranzan and Ooltul. Visitors from the surface are rare and tend to be viewed as potential slaves or food. Caravan travel brings mostly luxuries; staples must be grown locally.
Travel in the Middledark can be difficult. In many cases, its simply not possible to go from one place to another because no caves or tunnels lead in the right direction. To overcome this drawback, many of the races that dwell at this depth are prolific portal builders and tunnelers.
Surviving in the Middledark
The Middledark is, at its best, worse than the harshest surface deserts. The DC for any Survival check made in the Middledark automatically increases by 5, even for natives. Wild resources are hard to find, and most of those that do exist have already been placed under guard by someone else.
Glowing fungi and lichens are less common at this depth than they are in the Upperdark. They can be easily cultivated, but most concentrations of them appear in cities, not in the wild. Air tends to be stale, but breathable, though poisonous fumes choke out normal air in a few areas. In many places, water is scarce, and any large supply is well guarded. Creatures living at this depth get most or all of their water from the fluids in other creatures they eat. Food is the most plentiful of the necessities at this depth, but even that becomes an issue at the lower end of the depth range.
Denizens of the Middledark
No alliance is permanent in the Middledark. Some communities maintain wary trading partnerships with others, but it is understood that if one party ever grows stronger than the other, the terms of the partnership will change - perhaps drastically. Even in the most open of Middledark cities, newcomers can expect to be challenged (physically or otherwise) unless they make a pointed display of power upon entry.
Drow: Most drow cities occupy large vaults or caverns in the Middledark. At these depths, faerzress is common and powerful, and the dark elves have developed many potent spells and defenses that harness the Underdark's magical radiation for their own purposes. The Middledark also offers the defense of distance - a drow outpost near the surface is vulnerable to the attacks of adventurers and surface elves, but moving a large army into the Middledark can't be done with ease.
Taken as a whole, drow probably have the most significant presence in the Middledark. Their cities and strongholds are numerous, wealthy, and well situated for defense, and the drow themselves are cruel and strong. Only the endless feuding of the great Houses constrains drow power. Menzoberranzan is the most famous of drow cities.
Duergar: The Middledark is also home to the largest and most powerful gray dwarf realms. The duergar have no particular use for faerzress and do not worry about ages-old vendettas against the surface world; they came down to the Middledark because the lower one descends into the earth, the more rare and wondrous the minerals that one can find. If the Lowerdark were not so completely inhospitable, the gray dwarves would pursue their veins of ore and gemstones all the way to the roots of the world, but lower reaches of the Middledark represent the deepest depth at which large cities can be easily sustained.
Duergar cities are less numerous than those of the drow, but any given gray dwarf city is likely to be a strong, wealthy, and martially inclined realm quite powerful enough to deter the attacks of its hostile neighbors. The cities of Dunspeirrin and Gracklstugh are good examples of duergar realms.
Fomorians: The most hideous and wicked of giantkind; the terrible fomorians dwell throughout the Underdark, but mostly in the middle section. They are thankfully scarce, and no one knows of any true fomorian cities of holdings in the Realms Below. However, a few dozen fomorians gathered in a keep or clanhold represent a formidable threat to their neighbors.
Grells: Monstrous and alien, grells are usually thought of as solitary predators, but in the Underdark they have been known to gather in nests or hives numbering dozens of individuals. In settlements of this size, grells divide themselves into distinct castes, including a philosopher caste whose members boast potent abilities as psions or sorcerers. Grells make poor neighbors, since they regard all other creatures only as potential prey.
Grimlocks: Well suited for a life in the lightless depths, grimlocks gather in large, savage tribes that are fully capable of overwhelming the cities and strongholds of more sophisticated races. Grimlocks are tireless hunters and raiders, and they often range dozens of miles from their lairs in search of food and plunder. Like the goblins and orcs of the higher levels, grimlocks are frequently enslaved by other races (particularly mind flayers) and can he found almost anywhere.
The grimlocks long ago laid claim to the cavern complex called Fingerhome. Within it, the village of Reeshov is a good example of a community of free grimlocks, as is the Cavern of Cloven Heads, which is home to the twisted descendants of the Golden Eagle and Red Pony Uthgardt tribes.
Hook Horrors: These vile abominations plague many of the Middledark's lonely and deserted passages, waylaying any travelers who come along. Hook horrors seem barely sentient, but they have been known to gather in large and dangerous bands to stake out a good source of water or a cavern of edible fungus as their own.
Kuo-Toas: Kuo-toas are found throughout the seas of the Middledark. This once great race has dwindled over time, and many of kuo-toan cities lie in ruins. The worship of the Sea Mother is all-important in kuo-toan society, and kuo-toa clerics and monks wield virtually unchallenged power over the rest of the race. Kuo-toas get along reasonably well with most other Underdark races (except aboleths), and they travel widely as traders, pilgrims, and guides.
The strongest kuo-toan city remaining in Faerûn's Underdark is Sloopdilmonpolop, which lies in Old Shanatar. Kuo-toas generally keep to the saltwater seas of the Underdark, leaving the freshwater lakes to the aboleths.
Maurs: Like the stone giants or fomorians, maurs are not common, but where they walk, lesser folk get out of the way. Descendants of storm giants that were imprisoned deep in the earth long ago for some forgotten crime, maurs are unusual among Middledark races in that they are not malicious, predatory slaveholders. Some maurs are as wicked as any fomorian, of course, but for the most part, these ruined giants want nothing more than to be left alone by their neighbors.
Mind Flayers: After the drow, the mind flayers are probably the most powerful, notorious, and sinister of the Underdark's peoples. Illithid cities tend to be quite small by the standards of other races - few of them number more than 500 mind flayers. However, since illithids are uniquely well suited to hold great numbers of slaves and thralls, mind flayer cities may have ten times as many slaves as illithids. Unlike the slaves of the drow or duergar, illithid thralls are compelled to absolute loyalty and zeal in the service of their horrid masters. The mind flayers can field entire armies of thralls whenever they wish and hurl them into battle without concern for their loyalty or fighting spirit.
The mind flayers prefer the lower reaches of the Middledark, but they also have numerous communities in the Lowerdark. The mighty city of Oryndoll is the most famous of their realms.
Orogs: Stronger, smarter, and more advanced than their surface kin, the deep orcs are well suited for the fierce competition of the Underdark. Orog cities are not numerous, but they can be found throughout the northerly reaches of the Underdark, from the Spine of the World all the way to the Icerim Mountains. Orogs favor volcanic regions, so they tend to found their cities in torrid caverns too hostile for creatures without fire resistance to endure.
Umber Hulks: Although umber hulks are sentient, they are nomadic hunters that build no cities and manufacture no tools. Their claws and mandibles are more than sufficient for their purposes. Among the most common of the Underdark's monsters, umber hulks fearlessly attack almost anything they meet, relying on their confusing gaze to scatter or paralyze most of their foes.
No place on Toril is as strange and dangerous as the Lowerdark. This level of the Underdark extends from 10 miles below the surface to unfathomable depths and features a degree of strangeness that would drive some surface dwellers insane. Few upper-worlders ever descend to the Lowerdark, and few of the Lowerdark's denizens want anything to do with the surface world. Some of the creatures in the Lowerdark - intelligent or otherwise - aren't even aware of a surface world; others have heard of it but consider it a mythical place.
Interspecies and intraspecies strife is the rule in the Underdark. Resources are minimal, and weakness invites extermination. Most of the Lowerdark's denizens are chaotic, evil, or both. Even the vermin and animals encountered in this area are rarely ordinary - many have been transfigured by crossbreeding or magical interference. Nothing here is normal or simple.
Travel in the Lowerdark is arduous at best. The term Lower Underdark actually refers to many places, since the great domains of Faerûn's Underdark possess fewer and fewer interconnections the deeper one delves. Only about a third of the lowest sections of the Underdark actually connect to each other. The rest of the Lowerdark consists of isolated pockets of space reachable only from the Middledark, by water, or by transportation magic.
Typically only one route exists to any given point, and that is what must be used unless the traveler plans to dig one. Though time consuming and cumbersome, many adventurers find it expedient to do just that, so they keep the necessary magic items and spells handy to make their own tunnels as needed. Fortunately, faerzress is rare at this depth, so teleportation can be used to travel the Lowerdark with a reasonable hope of success, assuming that the traveler has a good sense of the destination.
Surviving in the Lowerdark
The Lowerdark is a strange realm warped by severe environmental and magical forces. The problems that pervade the rest of the Underdark intensify here. Resources are scarce, and control of them is continually contested. Air does filter down this far, but it is frequently stale and occasionally toxic because of geothermal fumes. Water is virtually nonexistent, and the little that is present is well guarded. Food cannot be found in the wild, unless the hunter has no aversion to cannibalism. (Many creatures at this depth survive by this means.) The Survival check DCs for most tasks increase by 10.
Exacerbating these problems still further are numerous areas of wild magic and dead magic. Though faerzress is rare here, the Weave in the Lowerdark is a snarled, tangled mess. Yet another magic-complicating feature is a high degree of Portal Seepage.
The darkness at this depth is so deep that it seems to actively dislike light. Natural light sources fail with unnerving frequency, and magical light sources draw attackers like flies to rotten fruit. In some places, the shadows cast in areas of light are unnatural - too large or too small for the light source, or cast in contradictory angles. Even beings with darkvision see a flickering of dark around the edges of their vision, as if the darkness were trying to drown out any sight at all.
Denizens of the Lowerdark
Why would any creature with intelligence or common sense live in such a terrible environment? Some races have lived here for generation upon generation, and the Lowerdark is simply their home. Other creatures settle here to take advantage of the Lowerdark's unique magical properties, rare ores, or shelter from the hated sun. Still others view a sojourn in the Lowerdark as a temporary solution, since the dead magic areas and hostile territory may be a wanted criminal's most expedient means of avoiding capture.
Of course, not everyone is in the Lowerdark by choice. Some unfortunates are here because they neglected to research the destinations of the portals through which they ventured. Others have been exiled here from communities in the Middledark, the Upperdark, or even the surface world. Some drow matrons get rid of potentially problematic subordinates by sending them on exploratory or expansionistic raiding parties into the Lowerdark. A triumphant scout returning from the mission into the depths might find her unexpected survival fatally inconvenient to the matron who dispatched her.
Several Middledark races make frequent forays into the Lowerdark. Some do so because of expansionistic desires, others because they need the resources, and a scant few because they have something to prove. Grimlocks and orogs often set a coming-of-age trial for their young warriors to mark the passage between adolescence and adulthood. In a typical version of such a trial, the youth is sent into the Lowerdark, sometimes armed only with a dagger, and told to return with a trophy demonstrating his competence and ability to contribute to the community.
Aboleths: These horrible aberrations lurk in the deepest, blackest waters of the Underdark, surrounded by legions of thralls. Gifted with extraordinary intelligence and powerful magical abilities, the aboleths are the unquestioned masters of most Lowerdark lakes and seas. While some aboleth cities are quite large, small outposts (or "broodholds") of a dozen or so outposts are much more common.
Avolakias: Thankfully few in number, the avolakias are master necromancers and shapechangers. In its true form, an avolakia is a 10-foot monstrosity combining insectile, octopoid, arid wormlike features. Devoted to the elevation of deities of decay and undeath (including Ghaunadaur and Velsharoon, among others), an avolakia nest is surrounded by a shambling army of undead under the monsters' control. Avolakias occasionally ally with aboleths or mind flayers, but they regard humanoids of any sort as nothing more than fodder for creating more undead.
Beholders: The Lowerdark is home to numerous beholder hives. Each of these bizarre cities can house hundreds of eye tyrants and thousands of slaves. Like mind flayers, beholders can magically compel loyalty from their thralls, and they believe that their natural role in the scheme of things is tyranny over lesser beings. Some beholder hives experiment with breeding strange servitor beholders to fill specific roles, but all eye tyrants believe that the beholder form is perfect, and that any deviation from it is monstrous. This attitude means that beholder hives make implacable enemies when they decide to go to war.
The city of Xonox, beneath the Lake of Steam, is an excellent example of a beholder realm.
Cloakers: Often encountered as small bands in higher portions of the Underdark, Cloakers gather into great convocations in a few places in the Middle and Lower Underdark. These strange and sinister creatures seem universally hostile to all other beings, and their teeming cities are no place for travelers to visit.
Deepspawn: These horrible creatures give birth to monstrosities of all sorts, surrounding themselves with armies of their spawned minions. Deepspawn are found in all portions of the Underdark, but the largest, most wicked, and most fecund of the species seem to hail from the Lowerdark.
Derro: Murderous and cruel, the derro are found at all depths of the Underdark. At the upper levels, they tend to live in small bands within the cities of other races, such as the duergar, fomorians, or kuo-toas. The true cities and strongholds of the derro are buried deep in the Lowerdark. From time to time, the derro muster their strength to fight great wars against all other creatures in the Underdark, swarming up from their hidden realms to plunder any realm unfortunate enough to lie in their path.
Desmodus: The desmodus are perhaps the only denizens of the Lowerdark that are actually good in alignment. The desmodus do not gather in great cities or strongholds; instead they live in small families and clans scattered throughout the Lowerdark. Even with their generally benevolent outbook, however, the desmodus do not take kindly to strangers raiding their food stores or water supplies.
Destrachans: These eyeless terrors roam the Lowerdark in hungry packs. Destrachans are the perfect Underdark predators. With their phenomenal sense of hearing and their sonic attacks, they are more than capable of stalking and slaying even well-armed parties of drow or surface adventurers.
Elementals: Elemental creatures and creatures with elemental heritage (such as genasi) generally do well in the Lowerdark. In particular, earth elementals and dust, earth, and salt mephits find the deep underground to be an ideal environment. Fire elementals, thoqqua, azer, salamanders and fire, magma, and steam mephits love Lowerdark regions with active volcanoes. Water elementals and water mephits occupy some of the sunless lakes and seas, while ooze mephit lurk at their fringes. Air elementals and air mephits are scarcer than the other varieties, but some can be found near portals to the Elemental Plane of Air.
Extraplanar Creatures: Portals in the Lowerdark open into almost every plane of existence. Often these portals are not marked or maintained, but just because the Faerûn side of the portal has fallen out of use does not mean that these doorways go unremarked at their destinations. Lone fiends such as bebiliths or hellcats often find the hunting better on the Material Plane than in their home realms, and some wind up staying.
Others outsiders sometimes use these portals to raid Toril. Demons, devils, and other types of outsiders use Lowerdark portals of varying ages to facilitate their travels.
Psurlons: Wormlike monsters with powerful psionic abilities, psurlons in the deep Underdark gather into communities known as clusters. Like beholders and mind flayers, they often dominate hundreds of useful thralls and set these unfortunate slaves to whatever tasks the psurlons deem needful at the time.
Tomb Tappers: Also known as thaalud, tomb tappers are huge constructs forged as weapons of war long ago. Intelligent and free-willed, these creatures hunger for magic and pursue magic items (and those who carry them) tirelessly.
Undead: Because undead creatures need no water, food, or air to survive, many of them find the Lowerdark almost hospitable. Liches are particularly common here, since they have no need to prey on the living and find that the Underdark offers blessed solitude for their sinister studies. Some of the mightiest liches eventually found small realms or kingdoms here. Such a kingdom could consist of hundreds or even thousands of mindless undead laborers and soldiers, led by creatures such as mummies, vampires, and wraiths.
At various depths in the Lowerdark (usually 15 miles or more); portals to the plane of Shadow become a new hazard for , travelers. Some sages theorize that the Underdark never ends; it simply becomes the Plane of Shadow at some immeasurable depth. This theory seems unlikely, although it is true that portals to the Plane of Shadow occur with increasing frequency the deeper explorers delve.
The shadow portals of the Lowerdark are always open and always active because they're actually holes to the Plane of Shadow. They usually subsume whatever tunnel or opening they exist in, and unwary travelers can easily walk straight through them. About 80% of these portals are two-way; thus a character who steps through and realizes the mistake can back-track before any harm comes. The other 20% are one-way portals that strand travelers in the blackness of Shadow until they can find another path out.
Fortunately, these portals are fairly easy to spot. A creature with darkvision can see the absence of rock on the other side of a portal, and one who depends on light can make a DC 13 Spot check to notice the way the illumination from a light source falls away into the darkness through the portal. A larger concern is that unless an explorer has an appropriate means to circumvent a Shadow portal, it effectively ends whatever tunnel it occupies.