Underground Sea

Despite holding such a beautiful name, the Underground Sea is nothing of the sort, instead being a toxic cavern full of noxious fumes bearing levels of acidity that can burn the skin from a dwarf in seconds. Never a popular travel destination, the Underground Sea rarely gets visitors, and the incredibly hostile terrain makes the area almost entirely uninhabitable. Being an infinite plane, the Underground Sea stretches for thousands of miles in every direction, eventually looping back on itself to trap those who would seek to leave its reaches by mundane means. Little else can be said of the area, being nothing more than a darkened cavern filled with all manner of toxic and acidic chemicals.
The cavern’s very wall are filled with these toxic minerals that constantly seeps from its cracks, turning to vapor on contact with the air, and filling the caves with fumes that cause intense sickness in those who spend more than a few hours breathing them. These vapors affect the water which the Underground Sea is named for as well, poisoning its reaches and turning it to a burning acid, made worse by the presence of naturally occuring poisons found on the seabed. Touching the water here is sure to result in the need for a healing potion, while ingesting it is likely to kill an unprepared creature outright, possible maiming them beyond repair.
Despite these challenges, the boundlessness of life can’t be kept down for long, and a few creatures have adapted to survive in the Sea’s caverns. Most are creatures found natively in the Underdark, adapted to resist the toxic vapors and acidic water of the cavern, while a smaller few are strange mutations of creatures that one might expect to otherwise find wandering the surface. Much of the life within the Underground Sea is relegated to living within the cracks of the cavern’s stone walls, but a few brave beasts have challenged themselves by learning to live in the acid-water of the cave, preying on each other and the few creatures that bother coming to the shore to drink. Of all these beasts, few present as terrifying a threat as Old Greyback, a strange sea-serpent similar in appearance to a remorhaz, with a chitinous shell that resist the acid water of the Underground Sea. Living in the cavern’s largest body of water, a place with no population to give it a name, Greyback spends each day swimming up the largest of the cavern’s streams, picking off food as it does so, before returning to its home at the end of each day. Never seen in full before, and once considered to have been only a legend, Old Greyback has likely been alive for centuries, and is thought to be over 120 feet long, with a weight of several hundred tons. No studies of Greyback have been done that allude to its origin, its level of intelligence, or the exact nature of the mystery that is how it has managed to survive so long in the harshness of the Underground Sea.

Type

Cave System