The only thing more foul than that which is below, is that which is above
They implored me to maintain hope. They were confident that I'd see my daughter again. But when I heard they'd turned their search to the Ontorlands, I realized their folly. My precious daughter is more likely to escape the grave than she is to escape the Nevyrback. And indeed, I believe she will escape neither.
Danye Kyatovy, Cervan empress, 3083 AoG
he Ontorlands are not a single location. Rather, the term refers, in aggregate, to all of the cave networks that are ubiquitous under most Excilior landmasses.
imestone is, by far, the most prevalent mineral under the planet's heavily-forested regions. And one of the planet's most striking features is the near-constant presence of rain. When this surfeit of runoff meets the abundance of soft, corruptible limestone lurking beneath the soil beds, the inevitable result is that much of this water ends up carving its way through the rock itself. Over the course of millions of years, the constant march of rainwater has slowly carved underground edifices that range from tiny veins of air and water, all the way up to gushing super-rivers that hew massive chambers and epic corridors in the underground foundations. Each of these underwater rivers can be thought of as a separate channel, flowing silently far below their surface cousins. Cognoscenti estimate that, for every river observed on the surface, there are at least two similarly-sized waterways running below ground.
A Vast Network
This is not to imply that the Onterlands are entirely submerged. Far from it. There are tens of thousands of kilometers of relatively-dry caverns and pathways in the Onterlands' labyrinthine structure. Every one of them has, at one time, served as a conduit for an underground waterway. But some of those subterranean streams have subsided to the point where they only take up a small percentage of their containing chambers. In other parts of the network, the edifices are now completely dry, with all prior hydraulics having long-since found other pathways and other chambers. Although water took eons to carve the edifices, the current network is a live-and-dynamic one. While some parts of the network have remained relatively-stable for millennia, there are entirely new sections of the cave system that are being actively excavated by the planet's rains to this very day. Although this is generally an epically-slow process - playing out over ages - this is not always the case. When a particularly strong waterway is suddenly diverted to a new headway of limestone, the water's carving process can be stunningly quick. Spelunkers have reported the creation of entirely new channels, spanning kilometers, within the narrow span of a few decades or less. The speed with which the limestone is etched away is generally dependent upon A) the volume of water directed at the stone, B) the force with which that water continually pelts the existing rock formation, and C) the possible presence of additional factors in the water that can increase its acidity.
he scope of the cave system is nearly as broad as that of the planet's entire landmass. Although there are many regions that contain no known connection to the Onterlands' network, it's generally assumed that this is only because the caves in that region have not yet been discovered, not because that region simply has no caves. Since the caves' formation is so closely aligned with the presence of limestone deposits in the underlying strata, it stands to reason that Onterlands caverns are more prevalent in regions known to have a higher concentration of the mineral. For this reason, known Onterlands networks are less plentiful in regions such as the high grasslands of northwestern Islegantuan, the Hammerhorn Mountains, and the Leung Peninsula. Nevertheless, Onterlands cave systems do exist in these regions. They are just fewer and farther between.
A Hidden Sea
One of the the cave systems' most mysterious features is not what's in them, but what's below them: the Ontorseia. This vast network of (possibly) connected saltwater reservoirs is a tangible barrier below which no human - neither Noctern nor oplander - has ever traversed. Whenever an Ontorlands explorer manages to go deep enough, eventually, they inevitably run into some outlet of the Ontorseia. Not that this bothers the Nocterns much. They have leveraged the waters' borderline-magical powers of preservation to lay their loved ones to rest. Deep under the planet's continents, millions of long-deceased Nocterns glow, silently, in the darkness, as they float peacefully on an eternal sea.
Ferrying passengers is rarely ever a profitable endeavor nowadays. No sooner have I quoted a price to a prospective client, than he has been pulled aside by some Onterlands huckster offering to guide him to his destination, underground, for half the price. I've given up explaining to them that they'll be dead in less than a week.
Tomi Rantanen, Lokkan merchant marine, 1919 AoE
he Onterlands have functioned, in certain regions, and at certain times, as a hidden system of de facto highways and trade routes. The tunnels and caverns branch and loop in so many directions that no one has ever come close to mapping the entire system. And the system itself is in constant flux. But the tunnels are so prolific that, with enough subterranean knowledge, bold explorers have managed to plot courses that run for well over 300 kilometers without ever peaking above ground level.
Passages to Nowhere
While it's unquestioned that the cave system is vast and intricately connected, that connectivity also becomes comically exaggerated - typically, for commercial gain. Enterprising explorers (and outright scam artists) have, in different historical periods, made bold claims about Onterlands passages that would ferry travelers wishing to remain discrete:
The hilarity of these claims does not stop there. More fanciful hucksters have even spun tales of Onterlands caverns that allow one to walk from the eastern shores of Islegantuan to the western shores of Isleprimoton, under the Sister Seia, under Sinum Balaena, and even north from Dinaisia clear under the equator and into "magical lands". Needless to say, all of these alleged routes can only be discovered if one is willing to pay a handsome fee to the guide, and none of the exaggerated claims of Onterlands interconnectivity have ever been verified. The physical requirements to maintain oxygenated, passable tunnels under great saltwater bodies probably makes the feat impossible. And even if it's technically feasible, the odds that nature has carved out just such a pathway, and that humans have managed to discover such a statistical oddity, are... unlikely, to say the least. This is not to say that some fabulous examples of interconnectivity do not exist in the Onterlands' vast - and often uncharted - corridors. It's even possible that some of these connections do, in fact, provide passage underneath major waterways.
For example, Onterlands networks that provide transit beneath rivers are plentiful and well-documented. Toterians, in particular, have utilized such caverns for millennia as an effective means to bypass expensive bridge construction. It's well-established that Onterlands tunnels connect the islands of Smugglers' Moot, but this is understandable since those islands are closely aligned and the waters between them are relatively shallow. In another tantalizing example, explorers have noted that the spotlite fish is only found in subterranean Onterlands caverns under the western and the eastern shores of Lake Orionton. This heavily implies that there are connected tunnels beneath the sizable lake that allow the same species to populate the subterranean pools on either side. Of course, even if it's assumed that there are, indeed, connected caverns beneath Lake Orionton, this also implies that those caverns are partly or (most likely) entirely submerged. So even if humans were to find these fabled passageways under the lake, they would probably be helpless to traverse them. This leads to a final obstacle to the concept of subterranean connectivity. Although thousands of kilometers of human-traversible pathways have been proven in the Osterlands' vast passages, there are thousands of tunnels that end not in a dead end - but in an ever-narrowing edifice that eventually makes human transit impossible. Do these diminishing paths eventually broaden back out into human-accessible tunnels (or something even larger)? Undoubtedly, some of them do. But many more probably just peter out into a tiny dead-end, far past the prying eyes of surface dwellers. And there's virtually no way to know which-is-which without having the benefit of some minuscule, water-breathing compatriot who can do forward-scouting on these diminutive tunnels.
Fauna & Flora
he Ontorlands is so vast that it easily qualifies as its own ecosystem. There are hundreds of known species (and probably many more hundreds of unknown species) that exist solely in this subterranean environment. Some of these species are clear analogs of their above-ground cousins. For example, the hairless homuhn looks similar to its arboreal ancestors, with the exception that it is smooth, white, nearly-blind, and features a stunning array of bioluminescent features. It also replaces its cousins' urge to build with a preternatural urge to dig/tunnel.
But there are many other plants and animals in the Onterlands which have no clear above-ground equivalent. There are four-legged fish that are just as comfortable lazing in a pitch-black pool as they are to drag themselves over the disintegrating limestone to the next viable body of water. There are insects that communicate - in patterns that border on higher intelligence - through intricate displays of light. There are slow, slogging, jelly-like creatures that spends decades feeding off the mineral deposits found on the cavern walls. There are mosses, that are found nowhere else above ground, and have been proven to heal the deadliest of human diseases. There are phosphorescent slimes that send signals to each other - over vast distances - by slapping the rock walls and absorbing the vibrations of others who are messaging them.
Hunters of Men
There is also a broad array of fauna that use the Onterlands as an effective "home base". They range out from surface snyres - typically, at night - and they drag their prey back into the dismal blackness of the Onterlands. Sometimes, this prey is consumed quickly. But many Onterlands predators have no formal "teeth" to speak of. Therefore, they must capture their prey, bind it in the depths with various forms of natural or biological webbing, and then either inject it with poison or cover it with acid. After the prey has languished in the darkness for days, dying a slow and excruciating death, the predator returns to slurp up the liquefied remains of its victim. In the deepest reaches of the networks' tunnels, the order of the day is utter blackness. The plants and the animals are all eerily similar - they are either white or translucent. The animals are not just blind - they long ago lost their eyes altogether. The plants rely almost entirely upon the consumption of biological detritus that falls to them from above, or they feed off thermo-chemical processes that emanate from deep in the planet's core.
But within 50 meters-or-so of the surface, the world of the Ontorlands is stunning for its light and its visual displays. This is because bioluminescence rules the day as a key survival strategy. Glowing algae pulsate through the waters. Animals deploy their innate lighting for mating and basic communication. Mosses secrete pulsing pools of light. Explorers have reported being able to sit by an underground tributary and read their own handwritten notes. The fluorescent hues often skew towards purples, blues, and pinks. This luminescent signature also makes the Ontorlands conspicuous in the nighttime forests throughout Excilior. The portals leading to the subterranean realm are typically easier to spot at night because of the faint glow of the pulsing life that resides deep below.
here are many natural resources gleaned from the Onterlands. The simplest would be water. Although rain falls plentifully above ground, the portals to the Onterlands can serve as easy collection points for freshwater.
The caves also serve as an invaluable source of exotic algae, mosses, fungi, and some fauna. Although the surface is replete with a myriad of species, there are many more varieties that can only be harvested below ground. Most of these crops are poorly understood. In fact, many of them can only be properly identified by the wisest of and most experienced cognoscenti. What looks like a life-saving root to a novice in the Onterlands can turn out to be a vicious poison once consumed. Nevertheless, the "magic" of the Onterlands' resources has kept thousands - some of them being sage cognoscenti, but many more being pure novices - ranging into the caves for millennia. In fact, a pilgrimage to the subterranean realm is often the last, desperate journey undertaken by those afflicted with chronic, fatal diseases who have exhausted all "traditional" approaches to a cure. These pitiful souls rarely meet a satisfying end - unless "satisfying" is being judged from the perspective of a hungry krawlr.
Some Onterlands regions are so vast that, inevitably, human populations came to take up permanent residence within them. Although these populations are only loosely connected, they are viewed, on "the surface", as a unified culture - the Nocterns. While it is entirely unfair to lump them all together, as a group, the Nocterns are easily one of the most feared and loathed civilizations on the entire planet. They are spoken of as boogeymen. They are used as cautionary tales to scare oplander children into (supposedly) moral behavior. They are killed for sport. A thousand fantastical and ridiculous legends are attributed to them. Just as they live in a subterranean society, they are viewed, by almost all of the oplanders, as being subhuman.