The Hollows are named after the mage that discovered them: Teragaius the Vagabond, who sometimes shares his name with the plane. (Pronounced teh-rah-GUY-uss.) They are (as far as initial impressions are concerned) a labyrinth of subterranean tunnels and shafts. But this is only because the surface is so dangerous. The sun rains a powerful curse on the land called Hollowfire. Everything it touches becomes cursed to die of a wasting disease, or to spread it to others.
The Hollows are part of one of the abstracted planes. This means that direct travel there is impossible--the plane can only be found by people who wander upon, usually through the tunnels beneath the Elterspine Mountains. Wandering, in this case, is strictly defined as unretracable travel. A traveler who has means to retrace his steps will never find the Hollows. However, even under conditions that meet this criterion, reaching the plane is as much a matter of luck as it is of anything else. Certain things can be done to improve one's chances, such as carrying artifacts native to the Hollows or casting chaotic spells that create a more random system of navigation. Failing that, anything that makes it easier for you to get lost will help you stumble into the Hollows (as well as any other abstracted plane). Mundane options include: running through the tunnels, blindfolding the party members most likely to remember the path, and getting completely inebriated.
The Deep Hollows
When the Hollows were first explored, it was not understood that they were on another plane. Few attempts were made to reach the surface (which we now know exists). Instead, early explorers focused on mapping the tunnel system. And indeed, many of the major features appear on Teragaius' earliest maps. The stone walls are made of volcanic stones (although no evidence of volcanic activity has ever been observed).
Perhaps the most notorious feature of the Deep Hollows is the gravity: the direction is variable. While it is not as noticible at the higher levels, there is a definite sway to the tunnels. Many report that it feels similar to being aboard a ship. When one travels deeper, the gravity may even "rock" so much as to seem to be coming from above. Since most of the tunnels are circular in cross-section (15'-25' diameter) this is not a problem unless there are loose rocks around (not infrequent). Naviation and travel are also difficult, since many horizontal tunnels can become vertical. However, this makes sleeping in the Deep Hollows problematic, since a sleeper will find themselves rolled all over the inside of the tunnel over the course of the night. With experience, a traveler can learn to sleep in the larger, smooth-walled tunnels. You simply have to get used to rolling over frequently and getting a sleeping bag very dirty (as it rolls over all the walls, twice). The Hollows are unique in that they have very few larger chambers--over 98% of the space in the Hollows is simply tunnel.
Deep Hollows Biota
Although Teragaius called the stringy material "blue moss" in his notes, the mages of today call the stuff by its proper name: Nalevexia. It resembles clumps of cobalt cobwebs from far away, and resembles broccoli heads from up close. It can be found in many of the tunnels, and in some of them it coats nearly all of the available surfaces of the tunnel. Oddly enough, in many instances the Nalavexia is organized into fractals or repeating patterns. The "moss" is not a moss--it is capable of muscular contraction, and will retreat from undesirable stimuli, such as cutting. Teragaius tried several times to obtain a sample of his "blue moss", but was hampered every time by the arrival of a Mole within minutes of his collection (surely not a coincidence).
Goldaundro Moles are enormous creatures that stand about 20' at the shoulders. They seem to navigate through the tunnels by echolocation, and their shrill shrieks can be heard long before they arrive. They possess forearms that are thick and paddle-like, much like a sea turtle's, with heavy digging claws at the end. If attacked, they crouch behind their broad forearms, pull their armored head into their bull-like neck, and swipe at their enemies. They usually do this in conjuction with their powerful magical attack: telekinesis (or localized gravity, which is impossible to tell them apart). Enemies are usually held in the air and battered at leisure. Certain larger Goldaundros have an especially deadly ability: Foes are held in the air and then spun rapidly. Extremely rapidly, in fact. Teragaius estimated that Helmenth (his least-favorite apprentice) was spinning at several tens of thousands of rotations per minute when his body finally flew apart.
Deep Hollows Locations
The Hot Spiral is a quartet of tunnels that spiral vertically. The incline of these spirals is steep--about a 30% grade. These four tunnels form a quadripartite helix that is packed very tightly. The walls between the helixes are thin enough that Teragaius could communicate between them by shouting. There is a dull roar coming from below that Teragaius sought to explore, but turned back when it grew too hot.
The Gremlin Stacks are one of the few open areas. It is about 150' in diameter and filled with icosahedral shapes with round holes bored into the center of their sides. The shapes are made of steel (or something harder) and are blunted from their constant rolling. Although Teragaius reported seeing small, gremlin-like creatures here, no other explorer has confirmed his report. It was in these stacks that Teragaius found the first of his glowing luminites (which we now know to be cursed). It was this first luminite that he affixed to the head of his staff and which probably lead directly to his death.
We know certain things about the surface. The air is extremely thin (similar to a mountain top). The temperature is extremely hot (another reason to avoid the surface during the day). And the red sun is extremely close (it dominates nearly half of the visible sky). Large parts of the surface are metal, or are coated with it. During the day, the patches of darker metal will heat up to several hundred degrees, which makes exploration of these metal "deserts" difficult. And of course, the entire surface is poisoned with a curse that lingers indefinitely and kills intractably. Perhaps I should elaborate on that.
The surface is covered with an extremely deadly substance called Hollowfire, which is emitted from the swollen sun. This "fire" is intangible, scentless, soundless, tasteless, and completely invisible in both the material and ethereal planes. It is an extremely powerful sort of curse that saturates objects (even air!) and radiates from everything that it has infected. It is so potent that it doesn't even detect as magic or a curse (perhaps due to the alien nature of the plane). Hundreds of curse removal spells and blessings have been cast on items infested with Hollowfire--all to no avail.
Exposure to Hollowfire may not cause immediate death, or even discomfort, but after days have passed, the curse matures into a wasting sickness that consumes the body from within. Death is inevitable. Exposure to large amounts of the Hollowfire will cause a feeling of prickling on exposed skin and the taste of metal. Early symptoms of moderate exposure: nausea, vomiting, hemophilia. If one is extremely badly burned by Hollowfire, however, only dizziness and tremors will occur. If this is the case, death will occur within the hour.
Methods have been developed by now that permit the detection of Hollowfire. The most reliable of these methods is Duskray's Golden Bird. This tiny, bird-shaped charm is worn around the neck. In the presence of Hollowfire, it will begin whistling like a shrill tea kettle. If the whistle is ever louder than a whisper, you are in danger.
Once cursed by Hollowfire, an item will remain cursed by it forever. Nearly all of Teragaius' belongings and notes are wreathed in powerful knots of Hollowfire, and can only be viewed remotely by wizards trained in the clairvoyant arts. Teragaius' research and artifacts are entombed in a secret place beneath Meltheria, underneath a foot of lead. Teragaius body is buried in the Northarm Cemetery in a lead-lined coffin. He was originally buried in the Starsought Vaults among his peers, but riots erupted, and many protested that his corpse would poison the tombs with Hollowfire.
I should explain. There was a powerful outcry after the curse was discovered on the artifacts that Teragaius had brought back. Despite his mastery of the art, the great wizard had determined that his "luminite" was non-magical and had given samples of it to many of his peers and friends. Since the nature of Hollowfire was not known, the glowing stones were given to wives as gifts, and children were allowed to play with the pretty, shining stones. All who were exposed to the Hollowfire are dead now, or close to death. To compound the tragedy, not all of the luminites were recovered, and many fear that the curse will eventually spread to cover the world if it is not buried deep in lead.
While the Deep Hollows are (relatively) free from Hollowfire, the surface is not. It is a well-established fact that Hollowfire radiates from that plane's sun. For this reason, travelers are advised to venture out only at night. Lead-lined cloaks and armor seems to be effective in resisting the burns of Hollowfire, but not perfect. Darkness spells seem to offer some limited immunity as well. (The Blood Cult of Mereskeld was known to have a potent spell that would wreath an individual in darkness, perhaps called the "Cloak of Shadows", which seems perfect for this application, but the paladins who have eradicated their cells have not retained the spells, nor have any of our attempts to contact a cultist been met with success.) The creatures native to the surface even seem to follow these precautions, since many of them appear to be metal or metal-coated. Even with these precautions (lead-lined hoods and cloaks, lead masks, nocturnal expeditions), travel to the surface is perilous due to the hostility of the intelligent races there.
The Carikel are mirror-skinned race of small creatures, averaging about 4' to 5'. Their faces have been described as "elvish vultures" although flamingos might be a more appropriate comparison. They have a graceful slant to their swept features, and although their beak seems avian, they have long ears ending in a tuft of bristling metal (possibly silver). Their eyes are large and intelligent, and they speak with songlike chirps and whistles. Whenever they are surprised, they reflexively create mirror images of themselves nearby. Their arms are slender and polished, and they have no wings. They fly using gliders, attack using their shortbows, or send out the Hetaliga when duty takes them underground. The arrowheads they shoot are covered in Hollowfire. Everything on the surface is. This makes it all the more important that arrowheads be removed promptly. They sleep during the night, and around noon nearly every single one of them can be seen swooping on their gliders in the powerful thermals.
Many of them wear necklaces studded with the glowing stones that Teragaius christened luminites. They make a paint from these stones, and paint patterns around the doorframes of their houses. Even the graffiti in Carikel cities glows in the dark. Some of them seem to use the glowing extracts as makeup, which makes their faces startling in the twilight. For the same reason, their books seem to be black pages with white ink made from the same substance, which allows them to read their books in the dark as well as in the light. Perhaps because of the availablility of metal, most of them wear layered shoulderpads and headdresses made from thin layers of metal that often resembles feathers.
It is not known what the original interaction was between Teragaius and the Carikel. We only know the result. The Carikel have issued several ultimatums demanding that we never intrude into the Hollows. Any trespass will be met with death. They also seem to blame us for the "loss of the little mirror", but it is not known if this refers to an actual item or a metaphor. Regardless, negotiations have broken down with them in recent years, and travelers from our plane are attacked on sight. This attitude was unfortunately reinforced recently when mercenaries from our plane kidnapped (and murdered) several Carikel as part of illegal research by an unscrupulous mage. Needless to say, we have not found many diplomats willing to go to the Hollows to explain these misunderstandings.
The Carikel take prisoners when possible. These prisoners are placed in the native legal system to be tried for their presumed crimes, but these captured individuals indoubtedly die within days from the curse of the Hollowfire. Attempts to explain the danger of Hollowire to the Carikel have failed, as have all attempts to negotiate for a cure to the Hollowfire curse. It is possible that they are immune, but I doubt that any curse this potent could be harmless. It seems far more likely to me that the Carikel are the creators of the Hollowfire curse, and have somehow bewitched their sun.
Little is known of their culture beyond this. The few buildings that we have seen have been tall cylinders of stone and metal. Their cattle seem to be the giant, flying, metallic jellyfish that are so ubiquitous on the surface. Their mounts are the mighty Hetaliga, which they ride by standing erect on their backs and gripping their armor plates with their strong feet.
The Hetaliga resemble stocky, metal-skinned worms about 15' long. They have the same proportions as a man's pointer finger. Their skin appears to be a heavy, mirror-like armor. This coat is very thick, and the Hetaliga are virtually invulnerable to damage while it is closed. Although both ends may appear to be identical, one end is the head. While the head-armor is closed, the worm has very poor senses--perhaps only sound. When the head is open, the worm's true face is revealed. This "true face" looks like a fleshy, red rose 5' across. This fleshy head has extremely acute senses, and can apparently sense heat as well as echolocate (perhaps similar to the Goldaundro Moles?). Conversely, this head is extremely fragile, and can be quickly killed by a well-aimed arrow once the creature has been baited into opening its head armor. Indeed, this is the preferred way to kill these creatures.
The Carikel use these creatures as hunter-killers, and send them down the tunnels in pursuit of targets. The hetaliga are capable of tracking prey for miles, so their senses must be formidable indeed. Although Hetaliga are capable of crushing blows from their armored termini, their preferred method of attack is to vomit superheated acid and/or stone (?) shards (reports are sketchy, and so far limited to field autopsies).
Lastly, the Tenzen Toads were first known as glowing creatures that abducted several people near the town of Tenzen, about a hundred miles south of Meltheria. Their origin was a mystery until a team of adventurers investigated them, and determined that they were actually natives of the Hollows. Back in the burning metal plains of their homeland, the marauding toads were joined by another group of the creatures, who fought intelligently before being driven off. After the attacks, many parts of Tenzen were determined to be cursed with Hollowfire. Two homes and a library have since been disposed of, as well as several thousand cubic feet of dirt. Since the mages have not had a chance to properly examine the "toads" or learn their proper name, the folk nomenclature of "Tenzen Toad" has stuck.
Tenzen Toads appear as slimy, bipedal frogs 10' tall, coated with (or made from) glowing yellow slime. They may have a variable number of limbs, and they may be able to change shape into a bulky ooze capable of swift movement. Regardless of what form they are in, the toads have huge, round yellow eyes that glow with a brilliant light (similar to Teragaius' luminites). Not surprisingly, these creatures are virtual infernos of Hollowfire. One of the adventurers who assisting in tracking these creatures back to the Hollows eventually developed the wasting sickness after being splashed with the blood of one of these things. Along with all of the kidnapping victims, he is dead.
It is not known how the toads interact with the Carikel.
0. The Liquor Out Of Space: This isn't a plot, it's a hazard. While trying to get from point A to point B along an underground route, the party has become lost and transferred to the Hollows of Teragaius! Everyone needs to get drunk and/or blindfolded so they can rush willy-nilly through tunnels until they get back to where they were going. They'll show up at point B stinko drunk. Complication: no one brought any booze. They'll have to make some. Or anything mind-altering, really. A few good hits on the head with a good, solid rock might do the trick. The alternative is wandering until they stumble back, which might take a very long time.
1. Battle Toads: Strange creatures have appeared around the town of Tenzen, kidnapping civilians and raiding the local library. After a messy battle with the creatures (giant, glowing slime-frogs) in the woods, the party is approached by a mage, yelling at the party to go bath in the river and throw away all of their clothing. They must get naked if they want to live! The mage explains (that he is not a pervert and) that the creatures have come from a place called the Hollows of Teragaius, and they must travel there to destroy whatever the toad-things are using to reach this place. The mage knows some good tunnels to get lost in, and he has enough moonshine for everyone.
2. Rock Collector: The party is sent by an unscrupulous wizard to collect some specimens of a new species on a new plane. He tells you that the creatures are evil bird-headed men who ride worms, and gives you a bag of holding to stuff their poisonous corpses into. He also gives you some heavy, spooky costumes to wear and tells you to avoid the sunlight, and don't spend more time on the surface than you have to. If you can bring back any of their books, he'll pay you their weight in gold. The party might discover that the creatures aren't evil, but they are definitely hostile. I guess this is the morality-based plot, huh?
3. Free Radicals: The party has learned about the race-war that that some mercenaries have provoked (if they weren't the mercenaries that did the kidnapping). They must rescue the imprisoned Carikel from a wizard and his mercenaries, return them to their homeland, and apologize. With godly diplomacy the party might be able bridge the gap between humans and Carikel, but more likely they'll be agressively jeered back into the tunnels.
4. Senseless Apprentice: Vetica, the favorite apprentice of Teragaius, has sent a message to her later master's compatriots. She has survived in the underground of the Hollows for all this time, and has vital news regarding the "blue moss". However, she has been captured by the Carikel, who are subjecting her to endless courtroom debates. They can't seem to decide whether to kill her or exile her. Luckily, she's convinced them to let her keep her lead-lined suit on, but she's not sure how much longer it will last. The party must sneak through the sleeping city of the Carikel (filled with domesticated, trained ant colonies and buildings shaped like metal cylinders, hemispheres, and platonic solids) and bust her out of jail.
5. The Princess Is In Another Castle: As above, except that she has been captured by the Tenzen Toads, and imprisoned in one of their semi-organic, earthen cysts in their bulbous mud-city. The party must sneak through the city at night, avoiding the toads (who are nocturnal and like to race in their slime form) and the omnipresent bath houses (filled with mercury).
6. Cloak of Finders Keepers: An enterprising wizard hires the party to infiltrate the Blood Cult of Mereskeld in order to learn the Cloak of Shadows spell, which will hopefully provide some protection against the Hollowfire that beats down from the infernal sun of the surface. The party will have to deal with disguising themselves as evil guys, paladins, and angry cultists (when their deception is discovered at the end). This is a little bare-bones, so you might want to combine it with #7 below, or blend it with another cultist plot (Maybe something from The Lavei Family?)
7. Marco Hollow: Bad pun. Anyway, the party is sent to map out part of the Hollows of Teragaius. Along the way the find evidence of an earlier human settlement in the Hollows from hundreds of years ago! Tucked away in a corner of a giant mushroom / flying spider forest (or was that a flying mushroom / giant spider forest?). Ancient scrolls describe combat with rushing blue phantasms, senseless gravity, and tunnels that shift before their eyes. They also reveal the truth about Nalevexia, the "blue moss". This scenario is a little bare-bones, too, so you should combine it with. . . any of the earlier ones, really.
8. Blue Miles: The party finally discovers that the blue moss, Nalevexia, is the fractured remnant of the planet-spanning super-organism (which includes the moles, oddly enough). If the party can clean out the Carikel and Tenzen Toads that are keeping the disparate segments of the creature from rejoining, the Nalevexia will regain its memories and intelligence. It will be smart enough to share the cure for the Hollowfire curse, which their wizard patron is dying from (or maybe a PC). It will effectively become the most powerful force on the planet (again), capable of summoning blue phantasms (projections of its will) and altering local bits of reality. I imagine it like an AI escaping into the net. All the party has to do is clear out a couple of subterranean strongholds of the Carikel and their warmachines. The Nalevexia also needs a hot reboot, which it can achieve by sending a few tendrils down into the planet's molten core. This endeavor is impeded by a race of magma-dwelling dire octopi that travel inside lava elementals. They must do this while the Carikel harry them from behind. At least they'll be aided by a few giant gravity-moles, and if they succeed they'll have a powerful ally and all the ancient lore their wizard patron could ever read.
8.5 Deep Blue: As above, except the Nalevexia turns out to be evil.
I swear I meant for this to be a short one.
The Hollows of Teragius are a pretty exotic place. Although it's intended for fantasy, it could be adapted for sci-fi pretty easily. One of my favorite things about this setting is how it turns the PCs into. . . well. . . orcs. They bigger than the graceful natives, they're scared of the sun, and they sneak around at night in heavy, ill-fitting armor. This is especially ironic if the PCs are there to kidnap some innocent bird people.
The blue moss, Nalevexia, is a lot more than it seems. It used to be a giant subterranean creature (like that 600 ton honey fungus in Oregon) that was all linked together. It's not a fungus or a plant, though, but rather a highly modified set of animal neurons (and support cells) created as an ancient experiment by a Carikel wizard called Yevishepsep, but he lost his sentience during the procedure (he got a lot dumber before he got a lot smarter). It actually grew quite hostile towards its former race, and created the Tenzen Toads to eliminate them. In the ensuing conflict, the Carikel destroyed most of Nalevexia, but since it was a superorganism stretching throughout the planet's crust, all they could do was chop it up. Now it exists as sort of a pest. It dominates the moles to guard it, when really it needs the domesticated ants to come and groom it (to get those synapses firing at a decent speed). If it ever linked up, it would be able to regain that cosmic intellect.
The Carikel are xenophobic and unreasonable, but they aren't evil. They've just had some bad experiences with humans in the past (more than wizards realize). Honestly, if someone doesn't want you there, you should probably leave, but enough good deeds and diplomacy can totally bridge the gap.
The toads are actually called Lhumox. Singular and plural. They're smart enough to tell you themselves, if anyone actually asked them.
If anyone thinks that giant telekinetic moles have an overpowered ability when they centrifuge people into exploding, I propose giving them a weak spot. You can't jump on the spinning person (that's silly and would make things worse), but I bet if you shot an arrow into the thing's eye it would lose its concentration. Alternatively, maybe centrifuging a PC just makes all his weapons fly out of his backpack, damage his friends, and scatter up and down the tunnel. After his friends fix his dislocated limbs, he can go pry them out of the walls.
And Hollowfire is radiation, natch! The planet's got a heck of a lot of gamma radiation coming in from the sun, and alpha and beta coming in from some of the elemental actinides down in the basement. That's why lead suits don't work so great in the sun, even though they're more than adequate in the tunnels. You don't see radiation in fantasy games because its so associated with sci-fi. But that's not a good excuse. Anyway, the Hollowfire curse is neat enough on its own anyway. If you changed a few things, the players might not even catch on that its radiation.