Far away from Tepui Mons (though connected underground to the same rock formation) lies a crater surrounded by kilometers of otherwise unremarkable pseudoforest. At its rim, it measures about 500 meters in width, though it widens into a slightly larger cavern immediately below the surface. In this twilight area, plants cling to the damp rock, with skystalks and basket-grasses growing atop mats of algae and moss that stabilize the thin soil. Descending further, the light gradually dissipates as the main opening of the Pit reaches over a kilometer down, tapering to a thin vertical tunnel at its base. Here, the sunlight from above is only a small circle, barely enough to illuminate the shiny rock below. Even here, a few clumps of moss and cyanobacteria eke out a living on the scant rays that shine upon them for just a few minutes each day. Despite the darkness, it's quite cozy at this layer; warmth noticeably emanates from the deep bedrock, while a draft keeps the oxygen flowing. The source of this cannot be seen, but it can be felt coming from a side tunnel jutting off to the north. This meanders for many kilometers, carrying a small but fast-flowing stream that trickles down from the cave's upper regions. It eventually dumps this water into a local river, where stirred-up bubbles float into the cave and provide life-giving air to its inhabitants.

Beginning in the Pit's twilight zone, the local life is quite similar to aboveground forms. Mosquitoes and woodlice can freely crawl or fly in and out, so this area has no endemic arthropods. Small rats make their way in regularly, and they too can often make their way back to the surface when necessary. There is only one flat terrace here; just above the thin lower section of the cave, a small plateau serves as the home for most of the upper cavern's flora. The only animal larger than a kilogram here is the Cave Kiwizelle (Cursoriapteryx troglodytes), a descendant of A. xanthopteryx whose genus is more common on the open plains further west. 300,000 years ago, when this species split off from the rest of its genus, the region around the Quarzkarst was not yet a full-on tropical rain-pseudoforest, but instead was a transitional zone between earlier tropical areas and the plains of the Ailuropian interior. This has resulted in S. troglodytes becoming stranded here, as suitable habitat can now no longer be found for many kilometers in any direction. From a small founding group, a stable population numbering in the 2000-3000 range now lives here. Such a number seems startlingly high for an area as small as the Pit. This is because, like the rest of the twilight zone fauna, the cave kiwizelle can exit the Pit when it desires, forage for food in the surrounding area, and return during the breeding season to raise its young. Only a few dozen individuals remain in the cave full-time, though this tendency is not inherited and seems to be determined by the level of crowding on the lower shelf. Even for those who venture outside, their underground home provides a much-needed refuge from otherwise inhospitable surroundings, especially when it comes to hatching their eggs far from the jaws of hungry predators. 

The only truly endemic twilight zone organisms are its plants. While many surface varieties make their homes here, dozens of species are found nowhere else on Apterra. In general, these are slow to diverge from their aboveground counterparts; once a plant colonizes the cave, its descendants are subject to one-way gene flow due to seeds continuing to make their way down from above. Novel mutations that arise here, though, are unlikely to spread to their cousins on the surface, so speciation can still occur with time. Nutrients are surprisingly abundant down here, as kiwi guano serves as energy-rich fertilizer. Without harsh wind, rain, or large herbivores to inflict damage, troglodyte plants are often softer than their relatives, and they're also more free to experiment with larger or smaller sizes. Insular dwarfism and gigantism have both taken place here; for example, a local swaystalk is only 30 centimeters tall, while a water-lily-like basket reaches three meters in diameter. 

The only environmental danger faced by the inhabitants of the twilight zone is occasional flooding during especially intense thunderstorms. This generally flows down the western face of the cavern, forming a waterfall that plunges into the semiabyssal zone below. Cave kiwis are wary of this threat, and young parents quickly learn not to lay their eggs on that side of the platform, while only a few small and hardy plants grow along the gulley formed over the millennia by this current. 

The thin, descending section of cave below the twilight zone, on the other hand, is completely submerged during the worst of these floods. As such, any creature that can't survive periods of up to an hour underwater will find itself unable to survive here. A species of sugarfly (Saccharoculex abyssalis) breeds here. The larvae eat detritus that washes down with the floodwaters, while adult individuals spend their time higher in the Pit, where they feed on skystalk secretions. Similarly, a pansanguinophage called Trogloculex cursoriovenator feeds on cave kiwis, returning to the semiabyssal zone to lay its eggs. Woodlice are also common here, including the subfluvial genus Troglarthrus, which has representatives both here and in the deeper sections of the Pit. While photosynthetic autotrophs provide a stable base for the semiabyssal food web, nutrients also regularly filter down from the upper levels. Manure and debris are washed into the lower chambers with each storm, and occasionally an unlucky cave kiwizelle will trip and fall from the ledge, providing a meal for the local carrion-isopods (Gehennarthrus abyssalis), which can't breathe water like Troglarthrus but have adapted to curl up and hold a bubble of air between their legs when the floodwaters arrive.

Entering the infernal zone, the temperature of the surrounding rock rises dramatically. Warm drafts make their way into the main cavern, but most of the heat remains trapped in this horizontal stretch of subsurface river. The worst of it occurs at its upper end, where warm, oxygen-rich air collects before spilling out into the semiabyssal and twilight areas. Gehennarthrus infernalis is the only animal that can live here full-time, feeding on the corpses of other creatures that succumb to the heat. Archaea grow both above and below the waterline, providing food for the Infernal Streamlouse (Troglarthrus infernalis), which emerges from the water for brief periods to feed before diving back in to cool off. It is preyed upon by the Knifetoothed Caveworm (Trogloculex deinodens), a neotenic mosquito that made its way into the infernal zone from the larger river downstream, and which is itself eaten by the Eyeless Hellwriggler (Infernichthys troglodytes), a ten-centimeter hunter and scavenger that's also happy to tear into any larger animals that get swept into the infernal zone. During feeding, it works its way into the body of its meal, eating it from the inside out. When it isn't eating, it swims alongside the Blind Rocksucker (Alveichthys archaeophagus), the descendant of a river-dwelling algivore that has now become specialized for eating the aquatic archaea of this region in lieu of its ancestors' preferred diet. 

In a few hospitable sections of the tunnel that rise permanently above the waterline, the Hellhole Rat (Tenuognathus adhaereus) clings to the slick rocks that overhang the rapids below. This descendant of Rattus platycauda snatches fish from below, employing the same feeding strategy as its ancestors but relying on its senses of hearing and scent instead of sight. Its flat, flexible tail allows it to swim easily from one air pocket to another, battling the fast-moving water to reach ideal perches from which to strike at its prey. It breeds in the cool, calm section near the outlet of the Pit, with females building nests to protect their pups while the males travel upstream to catch food for their mates. On occasion, young hellhole rats accidentally end up wandering out of the cave entirely, where they are almost always outcompeted by their surface-dwelling cousins or captured by sharp-sighted predators. Conversely, other members of Tenuognathus that aren't adapted for life in the Pit fare poorly against the specialist troglodytes. In general, immigration rates have slowed over time, as nearly all available niches in the Pit of Hell are now occupied by earlier pioneer clades.