Underhollow

The Underhollow is an expansive and perilous network of underground caverns and tunnels stretching beneath the surface of Osira and Tolria, shrouded in darkness and steeped in mystery. Once home to a myriad of creatures driven into the depths during the early ages of creation, the Underhollow has since become the domain of alien Illithid hives, whose parasitic presence has reshaped its already treacherous environment. These Mind Flayer colonies, stranded from the stars after rift anomalies caused their interstellar ships to crash, have taken to the damp and lightless depths to fester and propagate their parasitic hosts.

Environment and Geography

The Underhollow’s landscape is as diverse as it is dangerous. It ranges from narrow fissures that challenge even the smallest adventurers to crawl through, to massive underground lakes hiding coral caves, fungus forests, and bone-hewn caverns. Magma rivers cut fiery paths through the darkness, while ice-choked tunnels and hollowed chambers formed by geological upheaval create an ever-changing labyrinth. Earthquakes, volcanic activity, and underground flooding ensure that maps of the Underhollow quickly become obsolete.

Without sunlight, much of the Underhollow is enveloped in perpetual darkness, with only bioluminescent fungi, glowing crystal deposits, and phosphorescent lichens offering scant illumination. The silence is tomb-like and unnerving, broken only by the distant dripping of water, the rumble of shifting earth, or the occasional guttural cries of unseen creatures. For those venturing into its depths, the environment alone is a test of resolve, demanding extensive preparation and a strong will.

• Nearly pitch-black, the Underhollow necessitates magical or artificial light sources for surface dwellers.
• Trapped gases from volcanic activity and fissures make breathing hazardous, with explosive fumes and toxic miasma lurking in isolated chambers.
• Food and water are hard to find, with adventurers often relying on magical provisions or scavenging the perilous fungal forests.
• Earthquakes, collapsing tunnels, and sudden floods threaten explorers at every turn.

Inhabitants

The Underhollow is a haven for beings that thrive in its oppressive darkness and isolation. Chief among its inhabitants are:

• Illithid Hives: The most notorious residents, the Illithids (Mind Flayers), have carved out sprawling colonies in the Underhollow’s darkest recesses. After being stranded in the material plane through catastrophic rift collapses, these extraterrestrial invaders adapted to the subterranean world. Their colonies serve as breeding grounds for their tadpole hosts and as laboratories for their sinister experiments, with vast networks of thralls supporting their alien society.
• Deep Dwellers: Other creatures, such as Duergar, umber hulks, grimlocks, and hook horrors, roam the caverns as predators or scavengers. Their ability to navigate the terrain makes them formidable threats to unwary intruders.
• Luminous Fungi Forests: While not sentient, the fungal forests are a keystone of the Underhollow’s ecosystem, providing sustenance for many of its creatures. Some species are hallucinogenic, poisonous, or even predatory. Notably, the Myconid and their hivemind known as Big Moss have been known to thrive in these damp environments.

Infection of the Illithids

The Illithid presence in the Underhollow has deeply influenced its environment and the creatures within. Their use of psionic energy and Rift-borne technology has warped sections of the caverns, creating zones of heightened psychic activity, floating rock formations, and corrupted wildlife. Some parts of the Underhollow bear eerie remnants of their lost starships—twisted, organic-like structures fused into the natural rock, pulsing with alien energy.

Exploration

Venturing into the Underhollow is a perilous endeavor, suitable only for the most prepared and courageous adventurers. Its depths promise ancient secrets, untold riches, and powerful artifacts, but the risks are equally great. From navigating through labyrinthine tunnels to evading the ever-watchful Illithid hive-minds, every step deeper into the Underhollow brings new challenges.

The Underhollow remains an enigmatic realm, a haunting reminder of the fragility of mortal ventures and the creeping presence of forces far beyond comprehension.