Introduction What Is the Underdark Like?

INTRODUCTION WHAT IS THE UNDERDARK LIKE? The Underdark is the vast realm of interconnected To understand the Underdark, we must first caverns, passages, and tunnels, found far beneath understand real world caves. And to understand the surface of the earth. It is a place of no sun, no caves, we need to know how they are made. rain, and no change of seasons. It is, in fact, an almost timeless place, with any changes marked on a Cave Creation geological scale. That said, the Underdark is alive, in In the real world, most caves are created from the its own way. The slow drip of water “grows” limestone erosion of limestone, chalk, gypsum, and similar features, or wears solid stone away. Fungi grow in minerals. Rain water soaks into the ground, seeps place of grass, trees, and crops, while creatures of all into a seam of porous rock, and dissolves it, leaving types, many uniquely adapted to life underground, eat a cavity. This simple process is responsible for some both the fungi and each other. But more dangerous of the most dramatic and dynamic caves on Earth, yet are the civilizations that dwell and thrive in the such as Carlsbad Caverns, Mammoth Cave (the Underdark. The most benevolent of these are the longest cave system in the world), New Athos Cave dwarves, but there are also drow, kuo-toa, mind (the second largest cave in the world), Son Đoong flayers… and such aberrant denizens as aboleth and Cave (the largest cave in the world), and others. In beholders. Simply put, the Underdark is not to be addition, the dissolved limestone will eventually taken… lightly. leach out of the water, forming dramatic formations, such as stalagmites, stalactites, columns of solid HOW TO USE THIS PRODUCT stone, flowing masses of “drapery,” and ribbons of “bacon.” However, caves such as this can only form You can use the content found in Underdark where there is sufficient water. In arid areas, different Discoveries in several ways. For starters, it provides methods are required. you with numerous encounters you can use whenever your players ever enter the Underdark. Or, you can In areas where there is no water, the air itself can use the listed encounters to add some variety to more create caves. Strong winds can carry dust, sand, and mundane caves, lairs, mines, and tunnel systems. You gravel with it, slowly grinding a cave out of areas of should also feel free to adjust, alter, and expand upon softer rock (such as sandstone). Volcanic activity can each encounter as you see fit, tailoring each one to create what are called “lava tubes.” As molten rock your specific campaign world. Oh, and don’t always flows along, the outer surface will cool, while the depend on the dice. If you see a result you like on a liquid stone inside keeps going. These tubes can be table, use it, don’t worry about rolling for the result. It very long, with one in Hawai’i measuring more than is your game. Make the most of it. 40 miles in length. Glaciers can create similar caves, through the melting of ice within the glacier. As the As a final note, anything inbold refers to a stat water seeks an escape, it will work it way through the block in either the Monster Manual or Volo’s Guide to ice, washing out long passages. Monsters. Flowing water, washing along a slurry of stone and gravel, can create caves as well, even through the hardest of rock. The washing and grinding out of Gandalf: There are older and fouler things than Orcs softer stone can create what are known as “fracture in the deep places of the world. caves,” when the surrounding rock collapses. Finally, - The Fellowship of the Ring talus caves are the result of a rockfall, usually at the base of a cliff, and are usually made from unstable piles of stone. SampleIn the Underdark (and otherfile fantasy realms), caves and cave systems may be created artificially.

3 while fire elementals may be able to melt rock away. Tunneling creatures, such as ankhegs, umber hulks, and purple worms, can leave large passages, similar to lava tubes. Magic can be used to create caverns and cave-like structures, with such spells as stone shape and transmute rock. Finally, it is possible, especially in areas of strong or unstable magic, for the ground to shape itself into cave-like structures. Cave Formations As water in a cave flows along and evaporates, it leaves behind layers of minerals, which — over long periods of time, can form structures. These are known as speleothems (from the Greek spēlaion, meaning “cave” and théma, meaning “deposit”). Built up over hundreds and thousands of years, these structures come in a wide variety of shapes and sizes. A short list of cave formations is as follows: Dripstone: As the name indicates, dripping water creates these formations. Dripstone accumulations tend to be vertical and can often result in thick columns. • Stalactites are roughly cone- shaped structures that hang from ceilings. In the Underdark, piercers like to hide among The gods themselves may create caverns, perhaps stalactites. In addition, some through physical manifestations of their divine Underdark stalactites are immense, allowing them form or through the expression of their divine will. to be hollowed out and used as living quarters. Elementals may form caves as well. Earth elementals • Chandeliers are chaotic collections of stalactites can simply glide through stone, but many other that can form very complex structures. Dwarves beings fromSample the Elemental Plane of Earth can bore and deep gnomes may carefullyfile guide the growth through earth and rock with ease. Wind elements can of chandeliers to produce elaborately beautiful blast out holes, water elements can wash them out, creations.

4 • Helictites consist of a central stalk festooned Flowstone is akin to dripstone, but grows to look with gravity-defying branches, spirals, and twig- more like hanging curtains or sheets. like projections. They include formations with • Draperies, also known as curtains, hang from the such descriptive names as: butterflies, clumps ceiling and have a thin and wavy appearance. In the of worms, curly-fries, hands, ribbons, rods, and Underdark, draperies may become thick enough saws. As with chandeliers, dwarves and deep to serve dividers in a cave, forming rooms with gnomes may cultivate helictites the way a wood rippling walls. elf might guide the growth of a tree. • Bacon is a form of drapery that contains colored • Ribbons are stalactites that come in long strips bands. In Underdark areas of wild and unstable and greatly resemble their name. magic, it might even be edible. • Soda Straws are long and thin, with a cylindrical • Rimstone, also known as gours, is a flowstone shape, as opposed to the cone shape of regular buildup in cave pools. It often looks like semi- stalactites. As most fantasy campaigns don’t circular stairs, and may form large multi-level feature drinking straws, you may want to call terraces. As rimstone occurs in cave pools and them ‘grass stems’ instead. streams, it may create dams, leading to water-filled • Stalagmites are roughly cone-shaped structures that terraces. stand upright on the cavern floor. In the Underdark, • Stone Waterfalls are flowstone formations that ropers appear almost identical to stalagmites when look like river cataracts frozen in stone. In the their eyes and mouths are closed and they aren’t Underdark, these formation may actually be ancient moving. As with stalactites, Underdark stalagmites rivers turned to stone through the acts of the gods, can become large enough to be turned into guard elementals, or strong magic. posts, watch towers, and living quarters. • Broomsticks are vertically akin to soda straws, in Cave Crystals are formation of minerals in a that they are tall and thin. crystalline matrix. Normally, these structures are fairly small, although there is the Cave of the Crystals • Fried Eggs often look just like their name sake — in Mexico with gigantic crystal formations up to 40 they have a smooth rounded center and a rougher feet in length and weighing 50 tons or more. In the outer border. Underdark, similar crystals could easily be 400 feet in • Totem Poles are tall structures with segments, length (or even longer). showing the stalagmite’s various stages of growth. In the Underdark, these may server as markers, • Anthodites are clusters of needle-like crystals guide posts, and indicators of borders. radiating out from a central point (much like a flower). Often found on the ceiling of caves, • Columns occur when stalactites and a stalagmites individual needles may grow to be around three feet meet, or when a stalactite grows long enough to in length. The Cave of Swords, found in Mexico, reach the floor of a cave. Given enough time, a contains similar crystals up to six feet in length. column may become large enough to wall off a section of a cave. In the Underdark, truly immense • Dogtooth Spars are large crystals that grow to columns can become the equivalent of apartment resemble a dog’s teeth. They often appear in clumps, buildings. Usually the core is hollowed out to near flowing water. When appearing in dense contain a stairwell, then living spaces are carved out patches, dogtooth looks much like mounds of snow. of the rock, radiating out from the stairs. • Frostwork consists of growths of crystal with a feathery appearance. As the name indicates, it looks very much like frozen water. Can’t recall which is which between stalactites and • Moonmilk is comprised off limestone runoff. It is a stalagmites?Sample Just remember the following: c is for white in color, with a creamyfile consistency. Its exact ceiling and g is for ground. origins are unknown, and many be formed by seeping water dissolving limestone, or it might be

5 created via bacteria. In the Underdark, moonmilk may be edible, and could serve as a food source for LIVING IN THE UNDERDARK various subterranean creatures. The adventureOut of the Abyss goes into great detail on what its like to travel and explore the Other Objects Underdark. Even if you don’t plan on running • Calcite Rafts form on the surface of quiet bodies of Out of the Abyss, I highly recommend getting the water. They are comprised of white crystals, usually adventure anyway, if only for the material presented made from the mineral known as calcite. In the real in chapter 2, “Into Darkness.” The chapter discusses world such rafts are tiny — perhaps a few inches such elements of subterranean adventuring as travel in diameter at most. In the Underdark, such rafts speeds, general illumination, mapping, looking for could be immense, several feet thick and dozens food and water, and so on. That said, there is one to hundreds of feet across, and thus capable of subsection that needs to be expanded on — time- supporting a significant amount of weight. keeping. • Cave Pearls appear only when limestone can When exploring the Underdark — or any cave accumulate around a central point (such as a bit of for that matter — you are cut off from the sun and bone, tooth, or sand grains), while moving water sky. This means you no longer can keep track of time ensures the pearl can’t adhere to a surface. In the through such visual clues as the color of the sky, the Underdark, cave pearls may be made from more general light level, or the length of shadows. Thus, valuable materials then mere limestone, making you may have no idea how long you have been awake, them a form of Underdark gemstone. traveling, or resting. Experiments have shown that • Cave Popcorn consists of small spherical nodes of people with no access to the sun can have rather calcium-based minerals. It is usually white in color odd day-night cycles. For example, they may stay and comes in dense clusters. As popcorn may not awake for long periods of time (upwards of 24 hours quite fit in most fantasy campaigns, you may want to or more), sleep a normal eight hours, and then stay call this “cave coral” instead. As with moonmilk, in awake for another long period, severely warping their certain Underdark caves, popcorn may actually be sense of the passage of time. edible. In the Underdark, this may result characters • Snottites are as disgusting looking as they sound. staying awake for longer then they mean to. It also Comprised of colonies of bacteria, these slimy means they may be unable to accurately determine masses grow on cave walls and hang from the if they’ve taken a short or long rest (or an intended ceiling. They tend to be clear or white in color, and short rest may become a long rest). In addition, they in the Underdark may hide various oozes or slimes. will have no way of knowing if any of their magic You can find all of these formations (and many items have regained any spent charges, as they are more) in caves the world over. In addition, formations unable to see the dawn. Now, some spells will allow such as these should be common all through the them to tell how much time has passed — mage Underdark, and can be made of material far more armor, for example, lasts for eight hours. Once it exotic than limestone. Naturally, considering the size fades, the character who cast it will know that at least (and age) of the Underdark, many of the formations that much time has passed. listed can be far larger than noted. In addition, You may wish to have characters make Intelligence various Underdark races (such as deep gnomes, derro, (Nature) or Wisdom (Perception) checks in order to drow, duergar, dwarves, mind flayers, and so on) may determine the passage of time. However, as there are incorporate such formations into their dwellings and domains. Much like surface dwellers may tend to Any characters with the Keen Mind feat will be gardens of flowers, Underdark dwellers may tend to able to tell how many hours there until the next gardensSample of slow growing stone. file sunrise of sunset. See the Player’s Handbook, page 167.

6 few clues to work from, this should be a DC 25 (very hard) check. BUILDING UNDERDARK BEASTS Typical cave residents include bats, birds, bears, Along with not being able to tell exact time, lions, wolves, lizards, snakes, frogs, crabs, fish, characters in the Underdark can’t always be sure of salamanders, and numerous insects. Of these, the the light level. In a normal cave, there is usually no smaller animals (i.e. crabs, fish, insects, salamanders, light. Unless artificial light sources are used, the cave and the like) tend to be permanent cave dwellers, is pitch black. This translates to darkness — total while the larger animals are more transient, emerging darkness. The sort of darkness where a human can’t from the protective shelter of the cave to seek food see their hand in front of their face. This is equal to and water. the blinded condition. For transient animals, you can use most any beast However, in the absence of stimuli, the brain may listed in the Monster Manual as is. But for permanent supply some. Characters without darkvision, when residents of caves, you may want to make some subject to total darkness, may start to see colors that adjustments. For starters, cave dwelling animals aren’t there, points of light (that have no source), and tend to be a) blind, and b) white. In fact, among even movement. Curiously, experiments have shown those animals fully adapted to cave life, eyes are that some people (about 50% of the population) almost nonexistent. And since they don’t need to see, can “see” their limbs moving in total darkness. In protective coloration isn’t needed either, and thus the Underdark, any character who is trained in such animals aren’t just white, they are oftencolorless . Perception can “see” their limbs in front of their face, even in darkness. While this has almost no in-game Adventurers who encounter these animals will find effect, it may make such characters feel a little bit them to be small, pure white (or semi-transparent), better about their condition. and lacking anything resembling eyes. For insects and crustaceans, any antennae will be exceedingly As a final note, any character who lacks darkvision long, allowing the creature to feel its way around. and is subject to darkness for an extended period of As animals in the Underdark can be quite large, this time (at least a week or more), will find their other allows you to have an adventurer feel the touch of senses will start to compensate for their lack of sight. a long, whip-like feeler long before the animal it’s You can simulate this by allowing characters who attached appears. aren’t trained in Perception to use their proficiency bonus when making Wisdom (Perception) checks When building custom stat blocks for creatures based on hearing or touch. Characters who are (specifically beasts) of the Underdark, consider the trained in Perception make such checks at advantage. following: • Most cave dwellers should have a climbing speed. • As many cave-dwelling beasts are blind, Wisdom (Perception) and Dexterity (Stealth) are both common skills. • Any blind beast is immune to the blinded condition. However, due to a heightened sense of hearing, these same beasts may be vulnerable to thunder damage. • Blindsight and tremorsense are both common senses. • Special traits such as Keen Hearing and Spider Climb are common among cave dwellers. Sample Here is a sample stat blockfile for a cave-dwelling beast. You can easily modify other beasts to make them cave dwellers by using this as a basis.

7 GIANT CAVE BEETLE These flightless insects are common in larger caves and the upper levels of the Underdark. Blind and pale white in color, they are highly sensitive to changes in air pressure, which is how they “see” to hunt. Their antennae are easily twice as long as their bodies and are used to explore their surroundings. Scavengers, cave beetles will eat most anything, including live prey, carrion, and organic detritus.

GIANT CAVE BEETLE Small beast, unaligned Armor Class: 13 (natural armor) Hit Points: 9 (2d6 +2) Speed: 30 ft., climb 30 ft.

STR DEX CON INT WIS CHA 9 (-1) 12 (+1) 12 (+1) 1 (-5) 8 (-1) 3 (-4)

Skills: Perception +1, Stealth +3 Condition Immunities: blinded Senses: blindsight 30 ft (blind beyond this radius), tremorsense 15 ft., passive Perception 11 Languages: — Challenge: 1/8 (25 XP) Keen Hearing: The cave beetle has advantage on Wisdom (Perception) checks that rely on hearing. Spider Climb: The cave beetle can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check. ACTIONS Bite: Melee Weapon Attack: +1 to hit, reach 5 ft., one target.Sample Hit: 2 (1d6 - 1) slashing damage. file

8 5 While the chests are exactly as they appear to THE ENCOUNTERS be, the ceiling and walls are actually trappers. Probably the best way to use this chart is to add color to any expedition into the Underdark. Thus, 6 The chests are mimics, the ceiling you can either randomly roll to determine what the and walls are trappers. characters encounter, or you can select encounters 03-04 A corner of the cavern contains 1d6 oval that fit the nature of the adventure and setting. In objects, each about a foot long, attached to the addition, many of the results on this chart go beyond walls with webbing. Anyone who cuts into an the basic concept of a “random encounter” and are oval will release 1d4 swarm of spiders. small set pieces in their own right. Some can even be 05-06 This section of cavern tunnels contains a phase the basis for a short plot arc. However, no matter how spider nest. There are 2d4 adults, 4d4 young, and you use this encounter chart, use the results sparingly. 1d4 hatchlings. For adults use phase spiders, Having the characters constantly run into strange for young use giant wolf spiders. For recent and oddball objects, structures, locations, and the hatchlings use a swarm of spiders. Adjust numbers to fit your party’s challenge rating. Due to a phase like will rapidly rob these encounters of the qualities spider’s Ethereal Jaunt special trait, you may that make them so interesting; their unknown nature. wish to place the hatchlings in a totally enclosed If overused, these encounters will quickly become chamber, or one with extremely narrow entrances. old hat to the characters (and the players) and will 07-08 The cavern passage opens into a large chamber, invoke boredom, not apprehension, tension, and at least 50 feet across, which contains a bubbling wonderment. In other words: less is more. pool of lava at the center. There are two ways across — a narrow ledge that runs to either side of the pool or the narrow bridge that crosses the d100 Underdark Discoveries pool. The ledge requires 80 feet of movement if used to cross the chamber, while the bridge requires 01-02 A fissure in the wall leads to a room, 20 feet wide 40 feet. Characters that use the ledge must make by 30 feet long with a 10 foot ceiling. The floor, three successful DC 13 Dexterity checks (one at the walls, and ceiling made from close-fitting blocks of start, one at the middle and one at the end) to avoid stone. In side the room are two wooden chests. If slipping into the lava. Characters who use the bridge the characters investigate, they find the following: must make a single successful DC 16 Dexterity check (at the top of the bridge) to avoid slipping into d6 Room Contents the lava. Characters who crawl (in which each foot of movement costs 1 extra foot), use a climbing kit, 1 All is as it seems. The chests are empty, aside or otherwise take extra precautions can make the from dust and a few nondescript scraps. Dexterity checks at advantage. If a character’s armor gives them disadvantage on Stealth checks, then 2 All is as it seems. The chests contain 1d4 the Dexterity checks are made at disadvantage. trinkets (roll on the Trinket table on p. Any creature which falls into the lava takes 160-161 of the Player’s Handbook) and 6d10 fire damage when it enters the lava for coins suitable for the party’s challenge rating the first time on a turn or ends its turn there. (roll on the Individual Treasure table on p. 136 of the Dungeon Master’s Guide). 09-10 The passage opens into a spacious cavern. The ceiling is thickly populated with stalactites of all sizes and 3 All is as it seems. The chests contain 1d2 shapes. The floor contains a scattering of boulders, magic items (roll on the Treasure Horde table stalagmites, and general debris. Characters with a on p. 137-139 of the Dungeon Master’s Guide) passive Wisdom (Perception) score of 15 will notice and coins suitable for the party’s challenge bits of bone, chitin, and shell among the floor clutter. rating (roll on the Individual Treasure table on Characters who engage in an active search of the p. 136 of the Dungeon Master’s Guide). cavern find the bits with a successful DC 12 Wisdom (Perception) check. They may also find such things as 4 While the chamber is exactly as it appears coins, bits of metal, and other items as you see fit. Sampleto be, the two chests are both mimics. file

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