Call it what you will – the Underdark, the Darklands, something else, it doesn’t matter. In almost every fantasy game world, there’s an entire vast hidden land beneath the sunlit surface of the world. It’s a place of winding tunnels, fractured passages, and caverns that range from barely large enough to fit a party of adventurers and an angry monster to so vast that entire cities can fit inside with room to sprawl. It’s a place full of deep mystery, dark magic, and creatures both foul and fair. An entire world waiting to be discovered by explorers and adventurers, right underfoot.
Unfortunately, it gets handled as a short-term dungeon crawl, or a source of stock adversaries like the drow most of the time. It’s understandable; trying to run a campaign that spends a significant chunk of the time in the lightless depths isn’t the sort of thing most players are thinking of when they roll up their heroic door-kicker and treasure-finder.
So what reasons are there that could compel a group to try a campaign in the Lands Below?
It’s a new challenge.
Sometimes this is all it takes. Groups that have been playing together for ages will want to try something new – and when you’ve spent all your time in surface-built dungeons, mountainside dragon lairs, and rampaging through orc encampments, the challenges of the Lands Below are new and unique. Surface races – even those with darkvision – are at a disadantage in the eternal darkness. If your entire world is a circle with a 60′ radius, the noises outside that area get more worrying. Food and water can be a problem when you’re delving – sometimes even if you have someone who can conjure them. New foes, new dangers, new things to weigh the risk and reward of await the group that’s just looking for something new.
It’s a world full of exotic dangers.
On the surface, you know most of the things that are going to endanger you. In the darkness, even familiar dangers can seem strange. Is that pit natural, or did someone dig a deep pit and line the bottom with jagged stones in the middle of a tight passage for some reason? And is that reason ahead of you – or behind you?
More exotic hazards lurk, too. Sure, the grotto full of glowing fungi may be beautiful and send the spellcasters into excited fits about the things they can potentially make using them as components, but what about the spores they’re shedding, infesting you with a slow-acting disease? Or the hungry creatures that live amid the fungus, helping fertilize it by killing trespassers and dragging their corpses to where the fungus can colonize the remains easily? What do you do when you come out of a tunnel and a river of molten rock is sluggishly flowing through the cavern you’re in? When an earthquake hits, and now your group’s way back is sealed off by a collapse or a fault slip?
It’s full of strange prizes to be won.
Those glowing fungi might glow for a long time if you put them in a lantern with a little fertilizer, and that’s before the wizard works out how to preserve one and make an eerie eternal torch out of it. The druid might discover the mold nearby has curative properties, if you don’t mind smelling like damp rock for a week. Weird and exotic metals and gems of impressive size, never seen in the lands above, might be lying around for the taking – at least after whatever was living around them isn’t guarding them anymore.
Then there’s what the other creatures that live in the darkness might have made, insulated from the magical traditions of the lands above. Aboleths in lightless oceans might have developed magical grafts – pieces of flesh that bind to a living creature and give them some new power as if it were innate. Drow might have special wonders carved from some rare magic-soaked rock, letting them ignore gravity and walk on walls as easily as floors. Other races, more alien, might have things that defy understanding entirely, simply working because they do – and prone to failing for unexplained reasons.
It’s a perfect excuse to test new things.
Find a new class or new magic item you want to try out, but you’re not sure you want it in the campaign world at large? Introduce it as an option for the Lands Below. If it turns out to be more trouble than you thought, explain that it requires the magic-saturated nature of the subterranean world to let it work.
This also works for things you want to be strange, interesting, and rare. A novelty like a flat stone that grows hot enough to cook on when water is poured across it is something you might find in the depths, where things that can burn tend to be a lot rarer than on the surface. Some races, whose darkvision is thermal in nature, might even use such stones the way surface-dwellers use torches and candles, lighting their with a comfortable glow of warmth.
The creatures in the dark are stranger than strange.
Be it simple creatures or entire civilizations, nothing in the darkness has any reason to be like the things on the surface. When you have to carve living space out of the stone around you, space is always at a premium. Even the deep dwares and dark elves will have cities that look alien to the eyes of surface dwellers, with small homes carved into immense stalactite columns, pastures laden with fungal growths layered atop one another with sightless creatures foraging in them, and a cramped, claustrophobic feel.
The needs of such civilizations are likely to be just as strange as their living space. When you can find veins of precious metal while digging out a new room for your house, or jewels a king would kill for while trying to find a reliable source of clean water, conventional treasure isn’t going to be that interesting. A party that comes to a community of deep gnomes or skum with a decanter of endless water will find themselves with much more attention than a group that drags loads of gold coins in. Surface materials like hardwoods for carving would be valuable in turn as a luxury item. Groups looking to make a profit trading might want to think of surface things not known of in the darkness.
It’s usually the dumping ground of the surface.
Since the dawn of the gods, things best left undisturbed have been getting buried in the Lands Below. Powerful relics of divine wars, spells best forgotten, even dormant deities locked away for the safety of the world can occasionally be found in the depths. Some civilizations may even have come into being around these forgotten secrets – perhaps even descendants of those first commanded to safeguard the relic, who pass down stories of the lands above, long since stretched and twisted by generations of retelling.
Each and every such thing can serve any number of roles. Maybe the players need to find a dormant god of prophecy, who interred itself for when a band of worthy heroes would need advice from it. Maybe they need an ancient relic lost to time, a powerful artifact that the gods buried beneath miles of stone to keep it safe and prevent it from destroying the surface world. Or, perhaps, someone else is seeking the lost relic, and the players need to chase after them to keep them from getting their hands on it – sometimes those secrets were buried because they needed to stay that way, forever.
And sometimes the dangers in the dark went there to hide.
A lot of campaign worlds have some ancient prehuman empire that once ruled the world – serpentmen, aboleths, or worse. Sometimes those species went extinct or destroyed themselves, leaving nothing but mystifying ruins behind. Other times, though, they deliberately retreated into obscurity – often in response to things like the discovery of divine power by the younger races, or the first wielders of arcane magic.
These ancient nations may still lurk in the deepest darkness, laying eons-long plans to return to the surface and reclaim dominion across what was once rightfully theirs. Players who stumble onto a small operation on the surface may find themselves traveling into the Lands Below, seeking out the ancient cities where creatures older than their entire species have been laying traps and plots in hopes of being up to the challenge of upsetting those plans – and at least delaying them for a while longer, because who can truly stop creatures of that age and amoral malevolence?
Exploration can be its own reward.
The Lands Below are a frontier, as far as surface-dwellers are concerned, and one which rewards the curious with vistas that defy the comprehension of those used to the Lands Above. Caverns full of reflective crystal shards that turn even a single torch into a storm of dancing rainbow sparks, waterfalls cascading down the face of a cliff whose top and bottom are lost in darkness and mist, fields of softly luminous fungi and mold being browsed by eerily graceful creatures adapted to life down in the dark, and far more await the curious.
Those looking to explore and make a mark could do worse than to find a cavern not yet claimed by others and set to making their own kingdom in the darkness. With some inventiveness, a night sky of glimmering stars can hang above the nascent city-state, the city itself lit by the soft glow of glowing fungus-lights, alchemical lanterns, or eternal torches, while the citizens harvest the strange wonders of the Lands Below to share with the Lands Above.
New and strange places and dangers can be scary – and exciting.
The flip side of exploration is that the act of finding new places never before seen by surface eyes means finding mysteries and dangers never before encountered, either. A cliff that, on the surface, would just be an annoyance to climb becomes much more dangerous when you can only see so far above and below, with no idea how far up or down the surface extends. Caverns full of crystals are often hot, damp, and full of sharp edges. The twisting passages make sound play strange tricks, such that something breathing softly some distance away might sound as if a dozen creatures were panting in hunger just around the next turn in the passage.
Even the familiar becomes unfamiliar down here. Monsters can be reskinned into alien versions of themselves. Orcs become eyeless and ghostly pale, navigating by sound and creeping with inhuman stealth to ambush travelers. A wyvern loses its wings and gains the ability to leap like a massive cricket, its hide becoming chitinous and the tail segmented. Cattle covered in rough plates, scraping noisily at the mold on the rocks, is attended by something descended from humans, with vestigial eyes and a powerful sense of smell. The list of mild transformations of the familiar into the alien could go on almost forever.
If nothing else, the oldest reason of all – there’s treasure under those hills!
Even if they don’t value it, most civilizations will at least recognize gold and gems as something rarer than copper and iron, and likely keep some of it around out of curiosity if nothing else. This, in turn, gives the average adventurer the simplest reason of all to go questing into the Lands Below – the creatures down there are rich in a way that only kings can match in the Lands Above. Venture into the lightless depths, and you may return to the surface world rich enough to buy your own title and lands.
And with all the malevolent things that dwell in the dark, the players won’t need to spend much effort on justification of rampaging and looting their homes. Of course, you can still complicate things – if they find a drow infant in the wreckage, they have a tough choice – there aren’t going to be many in the surface lands willing to raise such a creature, returning it to the drow is likely to result in it being sacrificed or turned into another monstrous foe, and leaving it to die is about as unheroic a choice as one can make. So what does the band of supposed heroes do? (And really – isn’t a grand tale of raising a surface-dwelling dark elf hero just as much a treasure as the sacks of gold and silver?)