Once more unto the Morlocks: 20 lost civilisations of the underworld

I have a completely irrational love of weird underground human (or semi-human) civilisations. I'm not quite sure why. I think it's probably because of the vistas of deep time that they imply: of hidden cultures unfolding themselves into the darkness, generation on generation, gradually becoming stranger and stranger as they pass century after century completely isolated from the surface world. Dunkley Halton wrote some absolutely brilliant ones here.

Now, in the real world you'd have to be crazy to take your children and go and live at the bottom of a lightless cave system somewhere, because there's not enough food down there and you'd all end up starving to death. But the weird underground ecosystems and endless, almost entirely non-flooded cavern networks of D&D change everything: and while very few people would voluntarily choose to live in the underworld rather than on the surface in most D&D settings, once they're down there they can survive indefinitely if they have to, which effectively turns the Underdark into everyone's last resort place to retreat to in moments of acute crisis.

In reality, when everything falls apart people usually flee into the forests and the hills; but because there's only so much rough terrain available, they necessarily end up mingling with the descendants of all the other peoples who've fled up there in the past. But the D&D underworld is effectively limitless, and there's no reason why it couldn't absorb any number of waves of refugees, fallen dynasties, persecuted cults, displaced cultures, and so on, each new wave simply driving the others a little deeper down while still retaining its own distinct identity. In D&D-land, no culture ever really needs to become extinct. It just needs to find itself a deep enough cave to hide in.

Here are twenty weird (but human) underground cultures you might find in a D&D underworld, complete with (somewhat flimsy) explanations for why they're living underground in the first place. Makes a change from yet another bunch of deep gnomes, right?

1: Descendants of two ancient armies locked in stalemated trench warfare; both sides dug endless tunnels and counter-tunnels to undermine one another until they hit the underworld, and then they just kept going, the war by this time being all they knew. Now their mostly-collapsed trench networks reach miles underground, their semi-human descendants still blindly carrying on with their war in the depths of the earth, in the name of nations long since vanished from the surface world. Their culture is built around antiquated military ranks, and they have an instinctual and hysterical loathing of 'the enemy'.

2: A vast and ancient underground laboratory complex hermetically sealed itself after a disastrous accident, and was written off as lost by its parent culture. Most of the people inside were killed by the weird energies that they unleashed, but a handful survived, albeit mentally and physically warped by their experiences; and over the years that followed they created a tiny self-sustaining society within its walls. Thousands of years later, the laboratory's reactors finally failed and its powered doors hissed open at last, releasing their weirdly-mutated, lab-coat-wearing descendants into the underworld beyond...

3: Long ago, for reasons that must have seemed compelling at the times, an expedition was mounted into the depths of the underworld. Soldiers, sages, and explorers descended together far below the earth, where they slew many monsters and unearthed many treasures and discovered many secrets of the world below. But they went too deep: their numbers became depleted, their most powerful heroes perished, and cave-ins and hostile populations lay between them and the way home. Exhausted, they established a temporary base camp far below the earth, planning to restock their supplies and then return to the surface; but as years passed without a suitable opportunity arising, the hope of ever reaching their lost home receded ever-further into the distance. Some made a desperate scramble towards the surface, and perished en route; but others remained, and their old base camp has now grown into a small community, at the heart of which lie the honoured graves of the explorers who led their ancestors down there so many years ago. Their numbers have never been great, but they still possess many objects of power which were either carried down there by the original heroes or found by them in the course of their expedition, and with the aid of these they have been able to consistently hold their own against the creatures of the surrounding caves.

4: In the waning days of some ancient empire, a garrison of soldiers was stationed in the underworld to guard a strategically-important cave network against foes in the Underdark below. They successfully held the line against their enemies: but their parent civilisation was less fortunate, and as the empire fell their supply lines were cut and they lost all contact with the surface world. With no way of knowing what was going on and no route back to the surface, they dug in, fortified their position, and waited for further orders. Hundreds of years later their descendants are still there, furiously protecting their now fantastically-fortified cave network against all comers, and awaiting the now-mythical figure of 'the messenger' who will tell them that their watch is over and lead them back into the light.

5: Many years ago, a persecuted religious sect sought shelter in the underworld, hiding themselves from the surface world.  Down in the caves they have built themselves a sealed community built around strict religious principles, governed by their religious elders, and completely cut off from any 'corrupting' external influences. Their obsession with doctrinal purity weighs heavily upon the less devout members of their community, especially among the young; but living far beneath the surface means that would-be apostates effectively have nowhere to go, especially as they teach their children that the surface world is a nightmarish place full of bloodthirsty inquisitors who would burn them alive as soon as look at them. In fact, their sect has been virtually forgotten in the world above, its followers assumed to have all converted or perished in the great persecutions generations ago.

6: A century or so back, the ruling dynasty of a local kingdom was driven from the throne by a rival claimant. When the new king began hunting down surviving members of the defeated dynasty to make his claim secure, faithful servants fled with as many members of the family as they could find and hid themselves in the underworld, guarded by the most dedicated warriors from what remained of the royal army. Generations on, the descendants of this fallen dynasty still maintain a weird shadow court deep beneath the earth, insisting that they are the rightful rulers of the lands above. They still have their partisans in the kingdom, who swear their loyalty not to the king in the capital but 'the king beneath the earth'; and while its exact position is a closely-guarded secret, their cavern-court still somehow acts as a magnet to all kinds of exiles, rebels and malcontents who are no longer welcome in the kingdom itself.  

7: A terrible earthquake once tore open the earth, tipping an entire city into the abyss. By sheer fluke, a handful of its inhabitants survived the fall, only to find themselves stranded deep underground. Over the centuries that followed they and their descendants have gradually cleared and repopulated their shattered and jumbled city, making their homes in crashed palaces, inverted temples, and buildings that now stand at crazy diagonals. The language they speak has long since vanished from the surface world, and would be of great interest to scholars.

8: A criminal gang began using a nearby cave system as a hiding place and base of operations, concealing its entrance to protect them from the agents of the law. As their crimes became more brazen, and the hunt for their lair more intense, they began retreating deeper into the earth, surrendering the upper levels of their hiding place in order to conceal themselves ever further down. Now, centuries on, their descendants live far beneath the surface, and come creeping up through a dozen layers of concealed passages to conduct near-ritualised 'crime raids' on nearby communities on nights when the moon is dark. 

9: An ancient culture buried its kings and officials in a vast underground necropolis, with new tomb-complexes excavated to make room for each new arrival. They also believed that men and women of rank should have slaves buried alive with them, to serve them in the next life: a minor court official might just be buried with one, but a king might have a thousand or more. In the early days of the empire such live burial meant a miserable death from starvation in a sealed tomb: but by the time the empire reached its second millennium, the necropolis had become so vast that the slaves buried alive within it could (and often did) survive inside it for decades, living on weird crops grown from grain offerings interred with the high-ranking dead. Thus a bizarre community arose within the necropolis, its numbers bolstered by regular arrivals of new slaves: they called themselves 'the dead', and hid themselves from the living during their infrequent visits to the tombs, the marks of their presence being attributed instead to restless ghosts. Today the empire is waning fast: the tombs of its modern kings are paltry compared to those of their ancestors, and slaves are now too scarce to be wasted on live burial. But the 'dead' remain in their necropolis, living among the ruins of the tombs: they have long since converted the masoleums of the ancient kings into homes and workshops, improvising tools out of the grave goods buried with long-dead officials and courtiers. Their knowledge of the necropolis, and thus of the empire's history, is far greater than that of any living sages in the world outside.  

10: Centuries ago, invading armies drove the indigenous peoples of this region to the brink of extinction. To survive, they fled beneath the earth, modifying their traditional customs as best they could to fit in with their new environment. Today their descendants have thoroughly adapted to their new subterranean homeland, but they have not forgotten the loss of their original lands; they sometimes send scouts creeping up by night to keep track of developments on the surface, and as their numbers gradually grow, so does their confidence that their old territories might one day be retaken. Should the surface nations they once inhabited ever find themselves at a moment of acute crisis, then the secret armies beneath the earth may seize the opportunity to strike. 

Image by Mattpocalypse.

11: Long ago, a secretive organisation abducted a large number of people apparently at random, and imprisoned them within a large, sealed underground complex. There, they were systematically exposed to various weird substances (bizarre toxins, magical radiation, etc), apparently as part of some vast experiment: many died, but others demonstrated (or developed) surprising resistances, and were retained for further rounds of experimentation. Ultimately the staff who operated the complex were wiped out by some kind of bizarre pathogen, either released accidentally or deliberately unleashed upon them as a form of sabotage. But the experimental subjects survived, safe within their sealed environment: and while most starved over the months that followed, a handful of particularly hardy cannibals managed to hold out for long enough to establish a sustainable food supply within the complex, using weird plants fertilised with corpse-mulch and coaxed into growth by strange radiation. A few centuries on, their feral, mutated descendants - warped by entire generations of exposure to the substances which their kidnapped ancestors were only meant to be exposed to for a few months - have finally managed to tunnel out of their sealed prison, and escape through the plague-ravaged corridors of the outer facility into the underworld beyond...

12: A long-vanished culture with a taboo against capital punishment once punished its criminals by exiling them into the underworld, forcing them to march down a long tunnel that reached deep into the earth and then locking an immense iron door behind them. Their descendants still remain there, sealed beneath the earth, in loose tribal groupings based around the ancient crime syndicates, radical movements, and banned religions from which so many of their ancestors came. The great iron door remains as immoveable as ever, as it was enchanted to fill anyone approaching it from below with feelings of overwhelming terror; but over the years these subterranean 'crime tribes' have successfully mined their way into other parts of the underworld nearby. 

13: A saint of an ancient religion descended far into the underworld to live a life of ascetic contemplation, spending decades meditating in total darkness. After his death his followers established a shrine in the cave he had lived in, tended by an order of blind and silent monks and visited by occasional pilgrims who had been assigned particularly arduous penitential pilgrimages in punishment for their misdeeds. Gradually the keepers of this shrine developed a unique set of doctrinal irregularities, which they claimed to have been dictated to them by voices speaking out of the darkness; the high priests of their faith judged them to be ideologically impure, and the pilgrimages were discontinued. They were assumed to have died out centuries ago, but, in fact, their descendants and successors are still down there: tending to their ancient temple, perfecting their meditative techniques, guarding their crumbling libraries... and listening to the voices in the darkness. 

14: A mining settlement pursued a particularly deep vein of ore so deep into the earth that it became impractical for them to return to the surface each night; instead they carved out homes for themselves underground, passing whole weeks or months in the dark. As the decades passed the mines became deeper and deeper, and their links to the surface more tenuous, until finally the day came when the miners simply decided to cut out the middlemen and start selling their ore directly to the other inhabitants of the underworld, rather that bother with the enormous difficulties involved in shipping it up to the now-distant surface world above. Today they form a major part of the local underworld economy. Their kinsmen on the surface still have no idea why the ore deliveries stopped coming all those years ago.

15: An awful clan of incestuous degenerates was driven from their homes by neighbouring tribes, and forced to flee beneath the earth to survive. Down in the dark they became more freakish and inbred than ever, and several generation on they've devolved into a grotesque and twisted race, deformed and animalistic and insane. They sometimes creep out of their caves in search of food, preying indiscriminately upon humans and animals alike. The local population regard them as monstrous beasts: they set snares for them as they would for wolves or foxes, and would be shocked to learn that their ancestors were once ordinary humans.

16: Centuries ago, a work-gang of slaves labouring in a silver mine accidentally mined their way into part of the underworld. Reasoning that whatever was down there could hardly be any worse than their current existence, they secretly passed word of their discovery to their fellow miners; and at a prearranged signal, every work-gang in the mine murdered its overseers and fled down into the caves. Soldiers were sent to pursue them, and the escapees fled ever-downwards to evade them, retreating beneath the earth into weird subterranean labyrinths until they could no longer begin to guess the way back to the surface. Their descendants still live there today: they call themselves the Free People, and have used the mining skills taught to them by their slave ancestors to turn their caverns into an intricate and easily-defensible tunnel network, full of ore mines and fungus farms. They are tough and industrious and very good at keeping grudges, and in another few thousand years they may end up turning into dwarves.

17: A clan of hunter-gatherers once took shelter from the elements in a cave network, only to be trapped inside by a catastrophic cave-in. With nowhere else to go, they descended into the caverns, searching for another way out; but instead they simply wandered deeper and deeper into the underworld, until the way back to the surface was utterly lost. Turning their survival skills to their new environment, they became nomads of the underworld, roaming from cavern to cavern in search of fresh supplies of food: fungi to gather, cavefish to catch, and weird burrowing creatures to hunt and trap. Over the generations they became every bit at expert in surviving within their new environment as they once had been in the forests of the surface world; and while their legends still speak of a legendary world of lush green trees and abundant food, the young men and women of the clan increasingly view such tales as nothing more than a myth.

18: In some now-forgotten city of the ancient world, the castes were divided vertically: the aristocracy lived in a fantastical network of towers, never deigning to set foot upon the ground, while the commoners lived at surface level and the untouchables were banished to the tunnels and basements below, where they were expected to ensure that they were seen as little as possible by their social superiors. Years later, in an apocalyptic war with its rivals, the city was obliterated in a single night by a terrible magical bombardment: the only survivors were the untouchables, who cowered in their basements while the great towers crashed to the earth. Buried beneath a whole city's worth of magically-irradiated rubble, and fearful that their enemies would destroy them too if they gave any hint of having survived the fall of their city, the survivors decided that their only hope lay in digging downwards. They are still there, in what is now a great and hidden tunnel-cavern-realm whose highest virtue is secrecy, teaching their children in each generation that they will only survive if the world outside doesn't know that they are there. They possess near-supernatural talents for stealth, the use of which has ensured that no-one has ever found them to tell them that the war they're hiding from ended thousands of years ago.

19: On the shores of an underground sea lives an incongruous community of human fisher-folk, the boats of whose ancestors were washed down into the underworld by a tidal wave generations ago. With no way back to the surface they have established themselves down in the depths as best they can, illuminating their homes with stinking fish-oil lanterns, and living upon the blind albino cavefish and other, weirder creatures which live in the waters of their new home. The bravest of them have even constructed a makeshift whaling vessel from which to harpoon the monsters which swim in the depths of their lightless ocean, although the risks involved are terrible. 

20: Far beneath the surface of the earth, an ancient civilisation constructed a subterranean world for unguessable reasons of their own: a single immense cavern with its own magically-maintained artificial weather and climate, complete with a fake sun, moon, and stars which move across the cavern roof. The cavern is populated with plants and creatures, including humans, presumably descended from specimens taken from the surface world in distant prehistory, among which are some which have long since fallen victim to extinction on the surface world. The stone-age humans who live there simply take for granted that the world is a single cavern roughly a hundred miles across, and had no inkling that anything exists outside it - until, a few years ago, one of them went digging for flints and ended up accidentally mining his way into another tunnel network just outside. This has triggered something of an existential crisis for the people, but a handful of their bravest warriors have begun to conduct scouting missions into the caves beyond...