Araumycos

From forgottenrealms.wikia.com:

Araumycos (Dwarvish for “Great Fungus”) was an enormous fungal growth that lived in the Upper Northdark and lay beneath the High Forest between the cities of Menzoberranzan and Ched Nasad.

The nature of Araumycos is hotly debated among scholars. Its history is ancient even by elven reckoning, and no known origins have been confirmed. Even the gods refuse to answer any questions about the creature, and magic and psionics have no effect on it.

Araumycos

Lords of Faerun Kexizzoc