It is, amazingly, a single organism that exists in the region beneath the High Forest, beginning at a depth of one mile under the surface and ending at a depth of three miles. It is believed to extend from the Shining Falls to the Lost Peaks and from Tall Trees to the Hall of Four Ghosts, wholly occupying the labyrinth of tunnels and caverns that exist beneath the High Forest. The dwarves of ancient Ammarindar spoke of their mines located in the region beneath the elven realm of Eaerlann that were abandoned to the slow, inexorable growth of Araumycos. The elves have legends that date back farther still, linking the birth of Araumycos to the fell sorceries of the Vyshaantar Empire, but so little is known of that era, even among the long memories of the elves, that no origin can be conclusively determined. Araumycos is thought by some to be the oldest living creature on Toril; even the gods do not speak of it, and divine divinations regarding the titanic fungus always fail. Araumycos’s sentience is debatable; furthermore, it is immune to magic and greatly resistant to psionic energy. Some whisper that the creature is an avatar of Psilofyr, the lord of the myconids, but this is only a theory.
Araumycos houses many fungal creatures of all varieties. Colonies of fungus folk live within Araumycos and aggressively protect their domains. Travel within Araumycos is extremely difficult, as the fungus regenerates very quickly. Many passages and caves are blocked by the fungus’s bulging, gray-white masses that resemble giant accumulations of puffball fungus.
Although Araumycos is usually docile, it occasionally does lash out at intruders. It can use poison, insidious spores, and manifestations that resemble oozes and slimes in order to defend itself.
Once in a while, huge patches of Araumycos die for no apparent reason, revealing ancient civilizations long forgotten. Whenever this happens, surface and Underdark cities of the North send scouting parties to locate ancient artifacts that long lay buried. Parties of Shadovars from the Empire of Shade are especially interested in what lies buried beneath Araumycos, as they have burned away various portions of growth with acids, searching for something in particular.