Undervault

The Undervault is a sprawling labyrinth of underground passages and caverns that exists beneath the Basin of Life. It is host to an entire subterranean ecosystem that has flourished unseen for millennia, where the kephera - children of the Elder Goddess Keph - contained the vast Soulless Goddess Illith, the Leviathan. Unimaginably, Illith, the Leviathan, splintered herself into the illithoid race, who have broken free of their prison and are locked into a life-and-death struggle with the kephera. The Undervault is a strange continent separate from the Basin of Life, and is widely regarded as extraordinarily dangerous for even well-prepared adventurers.