What Lies Beneath

Vast caves underlay Serinarcta in the late hothouse, 290 MPE. Portals into this little-seen realm can be found across the continent, but watch your step, for few who enter will ever return.

There is a hidden world laying just beneath your feet across Serinarcta. A system of caves greater than anything ever before has hollowed out the earth beneath huge sections of the continent. They originated as hollowed-out seams in the rock where ancient coal deposits burned away in the great thaw, but have since been excavated out further on an incredible scale through the slow growth of cementrees. Ants living within these composite organisms must collect the sediment used in the creation of their cement-like building material from the ground around them; grain by grain, they mine it from the soil, leaving hollow pockets beneath the spires from which the trees ultimately grow. As isolated cementrees became spire forests, and these forests evolved into sky islands, the sheer amount of such aggregate removed from the ground over that time becomes hard to imagine. Some twenty million years of this slow process later, and vast, winding caves have been carved out below anywhere that cementrees grow in any number, but most spectacularly in the south and central region of the continent. Beneath the savannah woodlands lies a secret world of darkness, decay, and danger.

Serinarcta's deep cave systems lack primary producers, but don't need them. They are fed, in vast amounts, from the surface world's riches. Droppings from flying animals that feed in the upper world and roost below, regular inundations of nitrogen-rich floodwaters from wetlands, and frequent cave-ins that drop hapless animals into their depths all serve to introduce nutrients into their food chain. Serinarcta is pocketed with entrances into this underworld, ranging from holes just a few inches wide to chasms hundreds of meters across. A consequence of the immense scale of mining going on below the feet of each and every animal, sinkholes are commonplace, and often open beneath the largest animals of all, the gantuan herds, whose usually fatal introduction to the cave floor is like a whale fall, attracting scavengers from all corners of the underworld to feast. Most of the total area of these caves is still underwater, but over the course of the hothouse, the water table has lowered as many soglands have drained. Now the gutters of the continent, most caves of the late hothouse feature an upper level of winding tunnels, above subterranean rivers and lakes, which remain high and dry most of the time - an underground highway for creatures to traverse, searching for scraps of nourishment which fall down from above.

As a hostile herd of rubicond cygnosaurs moves through the woodlands, most creatures flee in their wake. A brindled birdbear flees up a cementree at first sight of the beasts, which will kill most anything that doesn't move out of their footsteps, as small ledgeleapers, a type of swift-footed loopalope adapted specifically to life on the edges of these sinkholes, quietly slip away into the grass to hide down the edges of a cave inlet, out of sight until the danger passes. Not everything flees the cygnosaurs - blue dungaroos follow the herds habitually as a way of life, usually confident in their agility to stay out of their way. So too do adolescent rasps, in between their days as internal parasites and arboreal predators, they fly along with the herds, biting their flesh and drinking their flood for nourishment. Only recently they matured and gnawed their way free from cocoons hidden in the muscle tissue of their hapless hosts; now they fly in the sunlit world, a life unrestrained.

But not all are so lucky. Freedom comes to some, but is lost to others.

Far below the activity above, one adolescent cygnosaur has slipped on the edge of the cave entrance and tumbled down to the mud below. It, too, is caught between two life stages. Just a few months ago, such a fall would not be a major pitfall - it would be able to clamber its way back up and out, a small and nimble juvenile. But now, it has grown too large. Still light enough to survive the fall down, this is no blessing - it has badly broken one hind leg. Try as it might, it cannot escape its prison, and after several more tumbles, it can only stand at the bottom of the cave and wail, a pained cry that scares several gloomswallows, a kind of gilltail bird, out of their daytime roost and into the daytime sky. It can't expect any assistance - cygnosaurs associate together purely for safety in numbers. Adults don't care for their young, or even recognize them. Altruism is not a trait they have ever needed. So from deep down in the darkness, anguished cries go heard by all, but cared about by none, as the herd continues on without so much as a backward glance. It is simply much easier, in their case, to breed again and bear new offspring, than to worry too much about the fate of any singular one.

But from inside the cave, others do come to investigate. The very first to come are the imps, cave-living foxtrotters that resemble goblins. They are inveterate scavengers, always the quickest to investigate anything which drops from the sunlit world into their domain, to see if it can somehow benefit them. They make their home high on the cave walls, out of reach of many cave creatures, and they climb with sticky palms and long, spindly grasping fingers. Huge, black eyes stare at the trapped cygnosaur, giving no clue as to their intent. One particularly bold individual, a mother carrying a pup on her back, descends all the way to the ground. As she climbs down over the titanic bones of an earlier cygnosaur visitor, she hisses and quickly sends a large fangworm slithering away - though such a predator could catch one imp, it knows that a group is a very dangerous enemy, for imps - unlike cygnosaurs - aggressively protect their own. This imp is the matriarch of her clan, their leader. Circling the cygnosaur, she chatters, and her clan grow more excited. She then changes her call, emitting a shrill, repetitive whistle which echos throughout the cave. This call is not to her own kind, but to another. It is a cross-species message. A dinner bell.

Minutes later, the stench of death fills the cave, instinctively terrifying the young cygnosaur, which attempts again to scratch at the steep walls and flee, to no success. A low rumbling builds into a rattling hiss, and the splash of water grows louder. The imp matriarch stands at the water's edge, staring ahead into the darkness too black for the cygnosaur to see. It cannot tell what is coming, only that it is very bad. When the imp turns and scurries back up to the top of the cave, she joins her group in watching the spectacle soon to unfold as the giant, eldest skuagator, trapped in this cave the very same way as the cygnosaur over 100 years ago, makes its debut, stepping slowly into the shaft of sunlight. The cygnosaur tries to run, but has nowhere to go. It was doomed the moment it slid down into the cave, for unlike the skuagator who can wait many weeks between meals, no suitable food for it can be expected to regularly descend from the skylight above into its jaws like manna from the heavens. Nearly its entire life has been spent down in the darkness; now very old, it is both blind and losing its sense of smell. Yet with no enemies to confront it here, no other skuagators to fight it off its territory, it still rules this part of the cave. And now guided to each new offering from above by the imps, it returns the favor by sharing its scraps with the small creatures that are simply not worth the time or effort to catch, for so little meat they hold.

All is over for the lost youngster in a few moments, as the old man of the cave catches its neck in its jaws and ends its ordeal in a second. It feeds eagerly but messily, tearing limbs and spilling the gut cavity, taking its favorite parts first, ignoring as the imps squeal and bicker over all the leftovers it leaves. These caves are a place of darkness, decay, and danger. They are a place of abundant death, too. Yet they are also a fascinating refuge for life, with interactions and adaptations unlike those anywhere else.

And this is only the tip of what lies beneath.