The earlier thread on the Night Below made me realize that the idea of a subterranean realm in Athas is something that’s probably come up on more than one occasion. So I thought I’d start a thread inquiring as to what thoughts people might have on the Athasian Underdark. If it would exist at all, how scarce the resources would be compared to the Forgotten Realms Underdark (the poster child for an underdark absolutely teeming with life), as well as what kinds of creatures would be appropriate for such a realm.
To kick off the thread I was going to start with my own rough notes on what I detailed for my own (very) homebrewed take on Athas.
"Chthonia is a strange realm of nightmares hidden beneath the burnt world of Athas. Although vast underground caverns have existed in Athas since time immemorial, Chthonia or the Chthonic Regions as we know them could never have come to existence without the interference of intelligent races. The core tunnels and caverns of Chthonia were first established by the Rhulisti during the crisis spawned by the brown tide. Seeking to escape the devastation the brown tide brought the Rhulisti established vast underground realms where the brown tide could not follow.
They used their life shaping talents to make the largest and most desirable caverns inhabitable for entire cities. The Rhulisti would go on to spread life throughout the underground caverns and tunnels, creating new and diverse fungus life that they could farm with relative ease, as well as hardy beasts that could survive underground without difficulty. A new ecosystem was blooming underground and the diminishment of the brown tide and construction of the Pristine Tower only magnified this flowering of new life. The Rhulisti took pains to connect their underground realms where they could, carving and expanding tunnels throughout the bones of Athas with the aid of fantastically crafted life shaped burrowers that are said to live in the Chthonic Regions to this day.
Eventually however the Rhulisti would fade from their underground realms, either seeking greener pastures above in the now flowering world or being driven out by new creatures that had come to call Chthonia home. It was in the Green Age when the Chthonic Regions would earn their name after all. The dwarves in their quest for greater riches would discover a harsh but strong ecosystem beneath their mines. They quickly realized the plants and beasts below could feed cities when properly cultivated and began establishing great stronghold cities inside the mountains of Athas.
As these communities began to thrive, humans too grew curious of the mysteries of the world beneath their feet and began various expeditions below the earth. However the insights of elves and men into the world below would prove paltry compared to the dwarvish achievements. The dwarven high king had his people build tunnels on an unheard of scale before or since that would connect all of their strongholds together. In time other races that inhabited the former Rhulisti cities would undergo similar projects on a far smaller scale. These dark paths represent the greater region of Cthonia that is heavily connected. However many large portions of Cthonia remain completely isolated to this day."
Chthonic Waters: Much of the water in Athas is buried underground, allowing for far more life to exist in Chthonia than one would ever imagine from a world as barren as Athas. Lakes and even a river or two actually exist in parts of Chthonia, however most water sources are unfortunately contaminated by minerals, making them undrinkable without proper filtration. However the fungus and animals nourished by the chthonic waters are another matter entirely.
Stygian Gates & Caverns: Aside from the dark paths, the chthonic regions have almost nothing keeping them connected to one another. Unlike the worlds of Toril or to a much lesser extent Oerth, portals are all but unheard of in Athas. However there is a strange anomaly within the chthonic regions that often connects them together, the so-called “Stygian Caverns”. These are underground caverns that exist in the gray, but not in the material plane, while others are sites where the gray and material plane bleed over completely. The openings to stygian caverns lead directly to the material plane and while some of these entrances and exits appear to be constantly active others require special activation through specific objects, spells, or phrases, making these so-called stygian gates very difficult to navigate. Creatures adapted to Chthonia have often learned how to open stygian gates naturally as well as survive in stygian caverns, either long enough to make it to another stygian gate or sometimes permanently survive in the stygian cavern if necessary. There are even known species of fungi that have spread to both the gray and the material plane, sharing a link with the two realms. Stories of stygian beasts that live as freely in the gray as they do in Chthonia are also whispered of.
Terrors of Chthonia
Caligni: Also known as Dark Men they are descended from refugees that fled underground to escape the Cleansing Wars. They made a deal with entities of The Black to allow them to survive underground. The creature of the black guided them to sources of food and water, yet the food and water the refugees consumed slowly changed them. Touched forever with the substance of the black the refugees would call themselves Caligni and under the direction of their false gods form a caste based society through which they would build thriving civilizations within the bones of Athas and observe the activities of the surface cities and their sorcerer kings.
Githyanki: Legends hold that the ancient progenitors of the Gith lived in fantastical gem studded cities below the earth. Supposedly these ancient Gith travelled to the moons of Athas and beyond in strange flying ships where they raided every realm they encountered as reavers, slavers, and mercenaries. What part they played in the Cleansing Wars is unknown, but no records of these ancient GIth exist after the Green Age. All that remains are their degenerate kindred and stories of their lost subterranean cities teeming with psionic treasures and the ancient moon gates of lost githyanki.
Morlocks: These strange humanoids appear to be massive devolved parodies of men with long apelike arms, flat noses, gleaming wideset eyes, shaggy pelts, and pointed teeth. They gladly devour any source of meat they can with a feral abandon that would give many thri-kreen pause. They shun daylight entirely and only emerge upon the surface of Athas at night where their shaggy hide protects them from the biting chill. Old legends claim that some towns sacrifice the lives of their own people in return for the morlock’s labor and protection.
Necropoli: Legends hold that entire civilsations of undead persist in the darkest corners of Cthonia, erected as grim parodies of the many legends of the afterlife. It is believed these necropoli are erected in or around the largest stygian caverns, where the grey overlaps completely with entire cthonic regions.
Neothelids: Within ancient cyclopean cities new and alien life slowly grows under the dominion of these wormlike horrors. Those unfortunate souls that are ensnared by a neothelid’s psionic at best can hope for their brain to be swiftly consumed. Otherwise they will be offered to the colony for ceremorphosis as a neothelid grub if inserted into the victim’s ear and they are slowly transformed into an illithid, the foul servants of the neothelid masters. Few psionic beings can match the neothelids and their illithid children in sheer psionic might and skill. Yet what foul agenda these terrible beings hold can only be guessed at.
Rhulisti: The oldest tunnels in Cthonia contain brightly colored walls as smooth as bone that lead to vast caverns teeming with fungi, running water, and strange round structures bristling with growths. What few accounts of these realms exist all attest to horrific monsters dwelling in these caverns that have never been seen anywhere else serving as primeval guardians of these lost lands.
Shardminds: On occasion explorers have encountered crystalline formations that ape the forms of men and beasts. Stranger still these crystals are potent psions and are capable of animating themselves entirely through their mastery of the Way. Little is known of their society, but they appear to be rather primitive and clannish.
Tari and Gith are both existing examples of races that would do just fine in Cthonia and I had a rough idea of Athasian Derro as a strange interbreed of gnomes and dwarves that were hiding from the cleansing wars. Additionally the idea that subterranian athasian trolls might have escaped the cleansing wars and became something very different is also quite appealing to me. However these ideas haven’t been fleshed out by me at all and I’m not sure if I’d even use them.