Archives of Candlekeep: The Underdark

Archives of Candlekeep: The Underdark

This article was first broadcast in Episode One Hundred Ninety on 24th November 2021.

Ryu (nervously): So…Lennon?
Lennon: Yes?
Ryu: You’ve done some traveling, right?
Lennon: Oh don’t remind me. It’s basically a piece of living geography, how do you lose track of a hill!?
Ryu: What?
Lennon: Sorry, fey patron issues. Right, traveling, you need some help packing? I recommend a towel. Possibly four.
Ryu (nervously): No…um…I was wondering if…you’d been to the Underdark?
Lennon: Um, not recently; my patron doesn’t have much business there, for obvious reasons. Why, you hoping I ran into someone you know?
Ryu: Well…not exactly…
Lennon: I don’t…oh hey, Ostron!
Ryu: No no! It’s noth-
Lennon: You been to the Underdark recently?
Ostron: Yes and no.
Lennon: Can you ever just give me a straight answer to a question?
Ostron: I give you straight answers all the time.
Lennon: Yes, fine, I’ll rephrase; can you give me a straight answer that is still an answer I expect to be possible when I ask the question?
Ostron: That sounds like a problem with your interrogation methods.
Lennon: Oh believe me; torture hasn’t been taken off the table yet.
Ostron: Why did you need to know if I was in the Underdark? Oh don’t tell me the shambling mound got down there somehow. It’s coming out covered in mushrooms, you know that?
Lennon: No, I think Ryu was looking for someone.
Ostron: Oh, okay, do you know where they are? Menzoberranzan, Doblunde?
Ryu: Um…okay so full disclosure…I asked about the Underdark because…I’ve never been there.
(pause, crickets chirping)
Ryu: All right, before either of you say anything, I want to remind you about racial stereotyping and judgmental assumptions and how bad all those are.
Ostron: Yes…granted…it’s just…well your situation seems to be a statistical anomaly.
Lennon: So what happened? Somebody drop something during a raid? Sent down a river in a reed basket?
Ryu: My mother just…moved above ground for some reason. There was a dragonborn community she settled near. There were a couple of raids after that, though, so they didn’t really like her.
Lennon: There are a lot of things that are starting to make sense now.
Ryu: Anyway…I know almost nothing about the Underdark and…a lot of people expect me to so I was wondering if there was a crash course or something?
Ostron: Um…okay…but this still might take a while.
Ryu: That’s okay; I brought my notebook and I hid all of Lennon’s notes on stuff going on in the world nearby, so we have nothing else to talk about.
Lennon: Hey!
Ostron: Okay then, I suppose we should get to it.

At a basic level the Underdark is a fairly simple concept; Underneath the surface of Toril and Oerth (the Forgotten Realms and Greyhawk, for those more familiar with the titular lands on those planets) is a basically endless and fully interconnected system of caverns, tunnels, and underground geography. The Underdark starts at about a mile below the surface, so while it takes a long time to mine your way there, existing passages that lead down to it don’t take very long to traverse, at least assuming you can deal with the darkness and don’t run into anything on your way down.

Vertically, there are sections of the Underdark that stretch down as far as 10 miles below the surface or more. At that point things get murky and there are stories of encounters both natural and not that prevent further progress.

In terms of real life creation, there doesn’t seem to have been a specific focus on making sure the Underdark was created and fleshed out as a concept by Gary Gygax. The first publication where the Underdark was mentioned was a series of original D&D adventures called the “D series” that were published in 1978. “Descent into the Depths of the Earth” is one we’ve mentioned before because in addition to introducing the Underdark, it was also the first known introduction of the Drow.

It’s actually hard to track the evolution of the Underdark’s mythos from there. A publication in 1986 called “Dungeoneer’s Survival Guide” seems to be the first time there was a publication focused explicitly on the Underdark. The tome first describes the Underdark (also called “underearth’ in some places) as being fully interconnected and inhabited by a range of beings who were mostly not fun to be around, and also calls out some notable locations, but it doesn’t describe a lot of the more supernatural elements the Underdark is now known for, such as living fungi and portals. In fact, other than the creatures mentioned, all of the challenges and risks of the Underdark according to the Survival Guide are simply those one would find in real life deep caves. Darkness, lack of air, pockets of harmful gasses, and instability from mining, quakes, and the occasional volcano.

As with so much of modern D&D a lot of details for the Underdark can trace their origins to the collected works of R.A. Salvatore, but the reality is the Underdark just became a fixture of most D&D worlds, so lots of different adventures, sourcebooks, and references would mention it and add elements to it as time went on, until it just sort of accumulated its lore by inertia.

The other interesting thing about the Underdark is that, like the D&D spell list, it seems to straddle multiple settings. Unlike the surfaces of Toril and Oerth the Underdark exists in both places and for the most part is largely the same. The only differences tend to be naming of specific settlements, but for the longest time whenever something was added to the Underdark it was effectively added for both Greyhawk and Faerun.

However practically speaking there has been a much larger focus on the Underdark in the Forgotten Realms than Greyhawk. As we mentioned in our profile on Greyhawk, a lot of that had to do with the spotty publication focus of the original setting. Also, obviously, with the popularity of Drzz’t Do’Urden, who is a Drow that hails from the Underdark, Ed Greenwood and R.A. Salvatore had more of a vested interest in fleshing out the details. For that reason, there’s usually been a setting resource published for the Underdark in every edition since 2nd: that edition had “Drizz’t Do’Urden’s guide to the Underdark.” “The Drow of the Underdark”, two publications with identical titles published for both 2nd and 3rd edition, focused mostly on the Drow, but those books had to flesh out more about the setting by necessity.

By the time you get to the 3s and 4th edition, there’s a resource for each simply entitled “Underdark” that covers the basics of the area and things in it, and why the Underdark is different from simply being a big cave. Of course, as usual, 4th edition added a few things to the lore of the Underdark that had never been seen before and aren’t acknowledged in 5th edition, although this is one of the cases where the 4th edition lore could still fit without directly contradicting anything that’s happened in 5th edition so far.

Now, again, those are just the sources that focused specifically on the Underdark. There are multiple other sourcebooks and adventures that reference the Underdark without focusing on it and add in locations, effects, creatures, and other things. For example in 5th edition, most of the information about how the Underdark works and what lives down there so far has to be pulled from the various Monster tomes (mostly the Monster Manual and Volo’s) as well as the adventure module “Out of the Abyss”.


Ryu: Oh, good! So you’re saying everyone else is as confused about the Underdark as I am.
Ostron: Um…probably not, on average. See despite all the different sources and such most of them don’t directly contradict each other. Like I said, even 4th edition’s Underdark didn’t really conflict with anything from before, it just added stuff, which is an accomplishment for 4th edition.
Ryu: Drat. We’ve got more stuff to go over, don’t we?
Lennon: Yep, here’s the first page.
Ryu: Would it be easier to just go down there?
Lennon & Ostron: NO!
Ryu: Okay…sorry…did I miss something?
Ostron: Just keep reading, it’ll make sense.m

Now to review all of the various information that exists, at least the parts of it everyone can seem to agree on.

The Underdark wasn’t created, per se, except in the sense that it’s part of the planet; it’s an accepted fact that once you go about a mile below the surface, you find the interconnected caverns, tunnels, and everything else of the Underdark. The formation is continuous, but you can’t always get through it; the Underdark morphs and changes just like subterranean areas of the real world. Caves collapse, magma flows deposit new rock material, seismic activity shifts things around, and every now and then a volcano decides it’s having a bad day and just rearranges a large part of the tunnel system. There are also a few creatures around that can add to the confusion, but we’ll get to those in a moment.

Now we get into the 4th edition lore we mentioned earlier. In that edition they created a god named Torog. His story is that during the Dawn War between the gods and the primordials, he was hunting down a primordial named Gargash. Gargash had fled into the Underdark to hide. Torog chased the primordial by literally bashing his way through the walls and caves of the Underdark. That scraped and broke him up pretty badly but he finally caught up to and defeated Gargash. Unfortunately for him, Gargash’s last gasp was to curse Torog to both not heal from his wounds and lose his power if he ever left the Underdark.

Torog tried to make his way back to the surface, only to discover the curse worked exactly as advertised. The other gods were less than sympathetic to his plight as he was no help to them in their war in his depowered state. Bitter and resentful, Torog retreated to the depths of the Underdark and became a god primarily devoted to death and torture. Meanwhile, his rampage through the Underdark created an unusually large and contiguous cavern that dips through all levels of the Underdark called “The King’s Highway.” This passage, unlike most of the Underdark, remains largely as-is due to the divine nature of its creation. It still loops around and about like the Gravely Hill Interchange, though, so it’s not like it’s easier to get around on.

As mentioned, nothing in 5th edition has directly contradicted any of that, although Torog is no longer listed as a god of Faerun in the Player’s Handbook. Also, interestingly, Torog made his way into Critical Role. He has largely the same role of an evil torture god whose domain is the Underdark, although his history is a bit different.

Now whether you want it to be there or not, we said the King’s Highway went through all levels of the Underdark. While the actual geography changes a lot, most sentients in D&D have developed a system of classification based on depth.

The upperdark is what most people think of as the Underdark. This is the area where the dwarves built a few cities once upon a time, there are a few other ruins around, you have a mix of Underdark natives and things that just wandered in from the outside, and so on. Basically this is the “tourist” level of the Underdark; kind of gives you the idea of what’s going on, but you aren’t really immersed in the culture. That said, a few of the larger settlements like Menzoberranzen are technically in the upperdark, albeit the lower parts of it.

From 3 to 10 miles below the surface, you have the Middledark. This is where a lot of the Drow settlements and cities are, a few cities of Duergar, as well as some of the more notable landmarks of the subterranean realm. This is arguably the “real” Underdark; anything you’ve heard of that makes the Underdark its home can probably be found in the Middledark somewhere, though how many of them can be found will vary with location.

The Middledark is also where you find two of the most prominent natural landmarks of the Underdark. The first is called the Labyrinth. A series of extra twisted lava tubes all connect and intertwine with each other in this area and create a very intricate maze. Reports vary between saying the area is 50 x 100 horizontal miles or 100 x 200 miles in area. This could be due to the nature of the shifting caverns and areas in the Underdark or just the reliability of the reporter. The caves also stretch up into the Upperdark in some places. Some parts of the Labyrinth have been improved with stairs and while there are some runes that supposedly provide direction, few if anyone can read them. Also, because it’s a humongous maze, it of course has attracted minotaurs, many of whom have been warped into hostile quazi-magic poisoned beings.

The other landmark in the Middledark is the Darklake. Somehow a 100 mile diameter cavern with ceilings up to 1000 feet has remained relatively intact in the Underdark and is filled with water deep enough to qualify as a lake. The water is traversable by boat, because duregar and kuo-toa do it regularly. They have a sort of uneasy truce with each other but will happily attack anyone else on the water. There are also water trolls, aggressive carnivorous manta-ray like creatures, and possibly dinosaurs in the water.

If you are suicidal or lost enough to go farther than 10 miles below the surface, you end up in the Lowerdark. The Lowerdark has the same sort of winding tunnels and obscure passages as the rest of the Underdark with the added bonus that it’s closer to areas where the fabric of reality is a bit thinner. That means you have the chance of finding portals to other planes of existence. Added to the fun, there are apparently a greater than average number of those portals that go to the Far Realm, which some people think is the reason there are so many beholders in the Underdark.

There are only two kinds of cities in the Lowerdark; there are messy, overgrown rotten smelling warrens and very intricate, spire like, multilevel constructs made from dark rock, smooth metal, and magic. You want the first kind.

The overgrown rotten settlements are the ones the myconids make, and they at least won’t attack and eat you unless you really tick them off by trying to put their children on your pizza or something. They’ll also eat you if you just drop dead in their house but that’s not really on them.

The nice fancy metal places weren’t put together by magic; they were actually put together with psionics and the people who did that are mindflayers. Mindflayers are the most populous species in the Lowerdark and almost anything that isn’t a mindflayer or a mushroom wandering around in the Lowerdark is probably enslaved to the mindflayers. I say “probably,” because if you don’t want your brain eaten by the squid people, you can instead jump in the water and get enslaved by the immortal mind-controlling megafish. That’s right, every body of water in the Lowerdark has a very good chance of containing one or more Aboleths who will happily rescue you from the mindflayers because they need slaves too.

Finally, if you’ve decided that the god Torog is still a thing, he crawls around in the Lowerdark looking for beings he can capture and drag away to one of the many torture dungeons he has set up down there.


Ryu: Okay, so what I’m getting here is, if you aren’t a creature that’s native to the Underdark, almost everything down there will want to kill or enslave you, and that’s only because they’ll like you less than the things that are supposed to be there, which they also want to kill or enslave. Are there any “fun” people in the Underdark?
Ostron: Maybe…mostly no.
Lennon (quietly): Hey you forgot about the-
Ostron: I didn’t forget, I consciously skipped them.
Lennon: They’re in the creature list, aren’t they?
Ostron: I think I took them out.
Lennon: You think?
Ryu: Hey guys what are the rest of these notes?
Lennon: That’s the dangerous things down there.
Ryu: Isn’t that just…everything except the walls?
Ostron: No, the walls are dangerous too.
Ryu: Well yeah, they sound like they get sharp and can fall on you.
Ostron: Also the radiation.
Ryu: The what now?
Lennon: Oh, yeah, this is another fun bit about the Underdark.


For no reason that anyone can really determine, the Underdark is suffused with a kind of magical radiation. Called “faerzress”, it seems to be naturally occurring but unlike real life radiation no one’s ever been able to determine the source. The effects are obvious, however. Areas with concentrations of faerzress have weird and unpredictable magic effects. It can be carefully harnessed to enhance magic with practice; most Drow cities have buildings and structures that only remain standing because of the faerzress in the area and the spells feeding off of it. But mostly what it does is make scrying the Underdark nearly impossible, teleporting unreliable and dangerous, and regular spellcasting risky for everyone. Long-term exposure seems to have some sort of effect, but it’s unpredictable. There are theories that it’s responsible for changing what spells the Drow are innately able to cast, allowed the Duergar to start doing magic even better than regular dwarves, and messed up some of the minotaurs in the Labyrinth, but again nobody’s certain. Doing a thaumaturgical project in the Underdark requires levels of insurance no one is willing to buy.

Now the Underdark isn’t universally bad news; you’ve basically got two bright spots as far as people you can run into. We already mentioned the myconids. The sapient mushrooms aren’t exactly eager to make friends, but they fall on the very short list of creatures and people that won’t immediately want to kill you. They will, as mentioned, happily eat you if you die near them though, so if you need to hide some bodies…no, going to the Underdark for that is still a bad idea.

Might explain some of the weirder half-memories I have from times when KayDee was doing things, though.

Oh, and I forgot, that’s normal myconids. If they happen to be the kind that actively worship Zuggtmoy, all bets are off and they’re definitely going to try to kill you too.

The other possibly friendly people in the Underdark are the svirfneblin, also called deep gnomes. Note, however, that being the only people not given over to regular murder and enslavement have made them wary of outsiders. The Drow hunt them for sport, the Duergar tolerate them sometimes but not always, and everything else in the Underdark sees them as much easier prey than going after something like a drider so they have hard lives. And there isn’t likely to be an armed force of svirfneblin willing to grant you asylum if you tick off someone else down there. But if you’re hopelessly lost, hungry, or in need of a good place to hide, a deep gnome will probably at least be willing to think about helping you.

We’ll quickly review the other sapient creatures because we’ve mentioned most of them already. The angry, magically mutated minotaurs are in the Labyrinth, mostly, but the entire Underdark is one big winding maze so they certainly aren’t limited to that area. The Drow are basically everywhere except the lowerdark and even that’s not guaranteed. The Duergar are only in slightly fewer places because they fight with the dwarves a lot more and don’t breed as quickly. One of their biggest cities is on the shores of the Darklake though so if you really need to find them for some reason, there you go.

We’ve already said that if you really want to get your mind melted head to the lowerdark and you can find all the aboleths and mindflayers you could ever want or need (which should be zero, by the way).


Ryu: Now if you want to temporarily lose your mind-hey!
(violent page rustling)
Ostron: Sorry, that’s not part of the notes, you don’t need that. 
Lennon: Here, I’ll hold it. Now just continue on with the rest of the notes. 
Ryu (suspiciously): Okay…


One of the species we haven’t talked about yet is the troglodytes. Similar to pale lizardmen in appearance, the troglodytes are far more primitive in behavior; they mostly use stone age tools and wander around the Underdark nomadically, rarely settling down. But all the moving and the hunting things the hard way means most of them are strong, and they are at least smart enough to follow basic instructions and learn simple tasks. That means almost everyone tries to enslave them, although they aren’t considered the most prized slaves. Again, they can only learn to do simple things and their natural body odor is foul enough to most creatures that it’s considered part of their weaponry.

Beholders are another fun friend you can make while you’re in the Underdark, except with a bulk discount option! It’s not uncommon to find random beholders sequestered away in all corners and caverns of the Underdark. Some of them carve out little kingdoms for themselves and feed their paranoia by believing everything in the Underdark is coming to kill them, which at least has the virtue of being true most of the time. Others will try to take over local groups of creatures and rule them. That tends to sort of work with troglodytes and svirfneblin, the former being easily convinced to follow anything stronger than them, and the latter being willing to make even a bad deal if it means someone stops everything else in the Underdark from killing them. The Beholders have slightly less success trying to control groups like Drow and Duregar.

Now the bulk discount thing that was mentioned; it has been reported at times that people found beholder colonies in areas of the Underdark. That’s right; large collections of beholders ostensibly working together, though to what purpose no one’s sure. Those have been in the lower areas of the Underdark so really you shouldn’t be going down far enough to find them anyway.

The kuo-toa are also a presence in the Underdark but mostly centered around Darklake for obvious reasons; other than the Darklake, finding potable water sources is kind of difficult down there so most of them don’t tend to wander very far, plus they have an uneasy truce with the Duergar mostly built around killing anything that isn’t them, so it’s a good deal for their purposes.

Rounding off the sapient species that make up a statistically significant population, you have the Fomorians. There’s not a lot about these guys that’s new; they’re giants, they’re underground, they hate anything that’s smaller or larger than they are, and they, yes, enslave all the beings they can to do work for them. They have lovely caves full of home-grown crystals though.

As far as non-sapient races go, there are a huge number of them; probably nine or more different species of creature in the Darklake alone, to start with, not to mention the random things that sometimes wander out of the portals you can find at random down there, so elementals and fiends aren’t out of the question, but we’re talking about natives.

Hook horrors are debatably sapient; they seem to operate in loose family groups ruled by the strongest female, but zoology expeditions to the Underdark need just as much insurance as the thaumaturgy  ones, so no one goes on those either. For the purposes of tourism, the main thing to know is hook horrors move in packs and claim territories, within which they hunt down and eat anything that even thinks about not being a rock, including the xorn that sometimes wander in from the plane of earth and start eating the rocks.

And finally you have everyone’s favorite creature / force of nature, the purple worm. The other major reason the geography of the Underdark sometimes changes without notice is that purple worms like to wander around the Underdark looking for food and they don’t let little things like solid walls of rock get in the way of that. In their hunt for a meal they will regularly leave 10 foot wide tunnels in their wake, opening up new and exciting ways for people to get around. Using any of those tunnels is a gamble, however, because the worms don’t necessarily burrow through the rock if they don’t need to; they’ll happily re-use the tunnels they’ve already bored out and that leaves anything else in them with a very large problem.


Ryu (ridiculously excited): Hey! Hey! Hey! Hey! 
Ostron: I thought you were going to hold onto that! 
Lennon: I did! I put it in my pocket! 
Ostron: When has your pocket ever been secure from Ryu? 
Ryu: There’s dragons! Two of them! Maybe three?

Thanks to the recent publication of Fizban’s Treasury, there are two confirmed species of dragon that can be encountered in the Underdark.

First, there’s the Sapphire dragons. These begemmed beauties aren’t guaranteed to be down there, but there’s a good chance. The sapphires like their lairs to be intricate and difficult to find cave systems and for those purposes the Underdark may as well be a model home show. They will largely be near the surface, so Upperdark or higher Middledark territory. But they hide their lairs with psionic barriers and reshaped stone so you probably aren’t going to find one unless you’re carrying around a really impressive or vintage piece of armor the dragon might like to add to its horde. The only other clue you might find to a Sapphire dragon being around is if there’s a curiously creature-less area of the caves; the Sapphires are even more territorial than the Hook Horrors, and they’re a lot better at killing almost everything in the Underdark.

The other dragons Fizban told us about are the Deep Dragons. Unfortunately they make their home in the not-fun areas of the Underdark; the lower Middledark and the Lowerdark. No one has figured out exactly why (see the notes above about zoology expeditions and insurance) but it’s very likely that prolonged exposure to the Faerzress coupled with the large number of fungus-like things in the Underdark have allowed the Deep Dragons to develop their unique ability to exhale breath made up of poisonous spores. Living underground and in the dark the dragons appear very worm-like, but they’re no less intelligent than most other dragons. Being so isolated, they hunger for knowledge of goings on both around them and in far-off lands. They then usually use that knowledge to stir up trouble and play their enemies off of each other. Or just if they’re bored and want some entertainment. Their minds and intelligence are enough that they are usually able to avoid trouble with the mindflayers and aboleths of the area, who are often the targets of their misinformation campaigns. If you do happen to find a dragon that’s run afoul of the mindflayers, though, just run.

Ryu: Okay so I’m only counting two types of dragon then, but guys! There’s dragons down there! I’m going to pack!
Ostron: I look away for one second.
Lennon: Oh like you could have held it better.
Ostron: She never pickpockets me!
Lennon: You never carry any money!
Ostron: Just finish up, will you?

Working the Underdark into a campaign is never really difficult; as mentioned, you just have to have something occurring that’s a bit deeper underground than usual, and any incident involving Drow, Duergar, mindflayers, or anything else considered native to the Underdark can easily end up there.

However, something to keep in mind is the point of the Underdark; it should feel more oppressive and overwhelming than just your standard dungeon or even megadungeon cave system. Unlike wandering into the lair of a wild beast that might or might not be aggressive or even going into a dragon’s home cavern, the Underdark has multiple dangerous and intelligent creatures working to disrupt the player characters’ goals, and that includes getting out of the Underdark to begin with. The presence of faerzress is supposed to be the key factor in that; by disrupting scrying and teleporting completely, it takes away one of the major methods characters could use to avoid getting lost. Also because spellcasting is unreliable, it can even disrupt spells like create food and water that adventurers might ordinarily use to avoid worrying about rations and supplies. Additionally, the roving purple worms, the random magic from nearly all the denizens of the place, and the natural seismic activity of a planet are supposed to be shifting and altering the caverns enough that a lot of natural pathfinding abilities like minotaurs’ labyrinthine recall don’t work. It doesn’t help to remember the path you’ve traveled if the path is gone or inaccessible a few hours later. Most adventuring parties might worry about whatever’s moved into old ruins or caves that they’re going to explore, but they won’t worry too much about the actual setting. Adventuring parties should be cautious about the Underdark just as a place, with the inhabitants as additional problems piled on.

It’s not widely advertised but the adventure module Out of the Abyss features an extended series of adventures in the Underdark, including a section that takes place on the Darklake. If you’re a DM who wants to have an adventure or campaign delve down there it’s worth having a look at some of the mechanics included in the module to see how it makes the Underdark a more difficult experience than a standard caving expedition.

Ryu: This isn’t standard! We’re going to find dragons! Ostron, fire up the magic!
Ostron: Um-
Ryu: Right, can’t teleport. See? I was listening! Oh! The audio alchemists are in a cave! Maybe that connects to the Underdark. I’ll be back in a second.
Lennon: If she lets the cat out again-
Ostron: The “cat” weighs 120 pounds and literally evolved to climb trees; a ladder and a floor hatch are not keeping it down there.
Lennon: Please tell me there’s no entrance to the Underdark down there.
Ostron: No, not anymore.
Lennon: Good that’s…what do you mean not anymore!?
Ostron: Mikey kept complaining about the noise.
Lennon: I…okay, what’s past is past, fine. I really have to stop asking questions around here. Let’s just go to the scrying pool.
Ostron: What about Ryu?
Lennon: I’m sure she’ll figure out there’s no way down to the Underdark from here and remember she has a job to do.
Ostron: She found out there’s dragons down there.
L (repeating tone exactly): I’m sure HR will have a Ryu join us shortly to make up for our wayward dracophile.