Ebonhollow Expanse

The Ebonhollow Expanse stands as the largest known cave system on the planet, intricately situated beneath the vast Arkynshire Lake, which holds the title of the largest freshwater lake. This remarkable cavern, along with the extensive lake above, was sculpted by the geological forces from a long-extinct maar volcano, creating a breathtaking blend of subterranean and surface water features.
Direct access to this stunning cave is primarily through a singular, majestic entrance located on a small, isolated island at the very heart of the lake. In addition, three other well-concealed entrances are nestled within the rugged hills that encircle the lake, each offering a unique perspective of the cave's grandeur.
Although the cavern lies predominantly beneath the lake's shimmering surface, its depths are impressive, extending deep into the ground and offering a substantial distance between the lakebed and the cavern's soaring ceilings. Geological engineers have conducted investigations and unearthed evidence of a substantial cave-in along the entire western flank of the sprawling cave. This geological event is believed to have occurred in the aftermath of the volcanic activity that shaped the cave, during a period when the magma subsided, and the cavern formed its intricate structure. Fortunately, experts currently assess the likelihood of further collapses as minimal, providing reassurance to those who wish to explore its depths.

Geography

The Ebonhollow Expance is a striking geological formation that originated from a maar volcano. Over countless millennia, the vigorous activity of the magma subsided, leaving behind an expansive subterranean cavern — a natural wonder that now serves as a testament to the region's volcanic history.
A significant geological event occurred long ago when the entire western side of the main chamber collapsed, resulting in a dramatic depression on the surface. This collapse effectively widened the Arkynshire Lake, which had formed around the main vent of the volcano. Over time, rainwater runoff accumulated, filling the depression and shaping the lake into the distinctive elongated form that is visible today.
The cavern itself features a main entrance from an island situated nearly at the center of Arkynshire Lake. This entrance, the remnant of the volcano's primary vent, presents a unique challenge for explorers. Navigating the twisting, labyrinthine hallways and vertical shafts can be quite arduous, as the pathways are narrow and treacherous. The passage ultimately culminates at the ceiling of the main chamber, transitioning into a sheer, staggering drop down to the cavern floor. To descend from this lofty entrance, one must engage in free-hanging repelling.
Aside from the main entrance, the Ebonhollow Expanse can be accessed through three additional ground-level openings. These alternative entrances, which were once side vents of the ancient volcano, provide easier access to the cavern, though it takes significantly longer to reach the main chamber from these points.
Nestled within the main chamber are mesmerizing areas of shallow pools, their surfaces glimmering as they reflect the ambient bioluminescent and caver's lights. Stalactites descend from the ceiling like a natural chandelier, while stalagmites rise from the ground, creating a breathtaking display of mineral formations. Flowstone cascades along the walls, resembling frozen waterfalls that have captured time itself in their intricate patterns.

Type

Cave System

Location under

Arkynshire

Inhabiting Species

• Brightgill

On the Map

Azlov

Open full size

The planet Azlov.

Ancient Remains

Dominating the main chamber is a large flat slab of rock that serves as a resting place for the skeletal remains of the largest ancient dragon ever discovered. Positioned somewhat centrally and towards the eastern expanse of the chamber, the bones are a testament to a creature of immense size and mystery.
Nearby, weathered inscriptions were found, their meanings obscured by the relentless passage of time. However, one particular section of stone has survived the ravages of the elements, revealing faint traces of proto-graphemes of the earliest form of the modern Draakhn language. Among the ancient dragonkin who have studied this artifact, there is a consensus that the dragon's name was Zar-Khos, a moniker that differs significantly from contemporary naming conventions among modern dragonkin.
Scholarly theories abound regarding the significance of Zar-Khos, with many believing that this remarkable individual may have been the creator of the fabled dragonstone. However, due to the inability to decipher the other inscriptions surrounding Zar-Khos's remains, the truth of this claim remains elusive. Additionally, it is postulated that the origins of the modern Draakhn language can be traced back to this sacred space. Yet, after the passage of possibly centuries or even a millennium, linguistic evolution has introduced substantial differences, complicating any direct connections to the ancient lexicon.
Near the ancient bones of the dragon, archaeologists have uncovered not only human remains but also a small, rudimentarily constructed settlement of tents, indicating that a group of humans once inhabited this subterranean refuge. This evidence suggests they may have been engaged in some form of worship centered around the ancient dragon, revered as a deity. Intriguingly, the human bones discovered do not appear to date back to the same era as the dragon remains, leading to the conclusion that Zar-Khos had likely died long before this group emerged to venerate him. The disparity in dating raises compelling questions about the mythos surrounding Zar-Khos and the reasons behind this community's seemingly desperate need to honor a creature that had long since perished.

Fauna & Flora

The Ebonhollow Expanse is a captivating subterranean realm, home to a remarkable diversity of fauna that has adapted to its unique and often harsh conditions. While the flora is sparse in this shadowy environment, an astonishing variety of fungi thrives, flourishing on decaying wood and organic detritus nestled within the cave's rocky crevices.
Among the myriad of fungal species, the notorious whitewyrm fungus stands out, known for its bone-white ribbon-like structure that extends vertically and weaves through the crevices of the cave floor. Additionally, emberglow puffball grows in clusters in the softer soils of the cave, its orange glow gently illuminating the ground. Parts of the ceiling are spotted with starspores, with faintly glowing spots on their mushrooms that sparkle like stars in the sky. The cave's walls are adorned with luminous brightgills that emit a vivid, ethereal light that can pierce the oppressive darkness, luring an assortment of small animals and insects. Notably, the Ebonhollow Expanse hosts some of the planet's largest mushrooms, which may have been thriving for centuries, their colossal caps a testament to the age-old ecosystem.
Inhabitants of this underground wonderland also include a diverse species of bats, which flit through the cavernous spaces, and large, agile rats that scavenge for food among the rocks. Among them are small, cave-dwelling Dragonkin, elusive and adept at navigating the labyrinthine tunnels. The vibrant ecosystem is further enriched by a multitude of insects, with the mushroomhoppers particularly notable for their attraction to the glowing mushrooms, such as the stunning Emerald Brightgill. These insects scurry in the warm, most air, adding movement and life to the otherwise tranquil landscape.

History

The historical significance of this cave to human activity spans deep into the past. Numerous legends speak of buried treasures concealed within the twisting side passages and chambers of its subterranean tunnels, some of which were hidden there by notorious pirates and other infamous figures throughout history. While only a few of the treasures have been unearthed, many still remain a mystery. Furthermore, these winding tunnels have also served as a clandestine route for the transport of illicit goods, allowing smugglers to navigate safely away from prying eyes. Some of these pathways bypassed the central chamber, maintaining a veil of secrecy over their operations. However, the discovery of ancient skeletal dragon remains in the main chamber within the cave marked a turning point; the once-thriving underground activity abruptly ceased, supplanted by the influx of scientists and tourists drawn to the awe-inspiring geological features and rich history enveloping the cave. This shift brought an end to the shadows of illicit dealings, transforming the subterranean world into a site of academic study and public fascination.

Trivia

The Ebonhollow Expanse was inspired by Blackreach from Skyrim.^[1] This cave may not also spark joy.

References

1. "Skyrim:Blackreach" - on UESP wiki; December 8, 2025.