The Krephus Passage was created in the Dawn Era. It was created when a colossal primordial worm named Krephus escaped the Step of Foundation. Aftering boring its way through the Web of Magic, it found itself on another world. On Bal-Kriav's continent Hezmort, it dug down, leaving behind the great bore hole named after it, the Krephus Sink. In her wake, Krephus left a wide cylinder passage that crosses many continents, dives into the Underdark beneath oceans, ending in the Underdark region Badmaer where she died.
At its northern tip in the Badmaer region, where the passage joins with the cavern complex Vogelak, is where Krephus breathed her last. The last 900' of this tunnel, roughly 60' across, is the petrified body of Krephus. Upon her death, a spell was triggered that magically petrified her body (put on her by Hon'palos). Krephus's body became stone as hard as any diamond. Foreigners entering this northern tract of the Krephus Passage often don't even realize their traveling through the body of a petrified primordial purple worm.
In the God Era, gnomes fleeing the demon hordes of Jurusalax, went into Krephus Sink. They followed the Krephus Passage to the Earth Seam, escaping by way of the Baruk-Agan portal.