The Cavern of Black Blood is an extremely dangerous and desolate region of the Underdark.
This enormous cavern is over 250 miles in diameter and contains many ancient ruins, including cities and temples long forgotten. Its name derives from the inky, tar-like substance found here. In the center of the cavern is an enormous lake of this black blood called the "Caltherium."
Temple of the Faceless God
One of the most horrific structures in this cavern is an ancient temple to a forgotten deity known only as "the Faceless God." An inscription on the base of the ruined temple says the following:
They worshiped, so they said, the Great Old Ones who lived ages before there were any men, and who came to the young world out of the sky. Those Old Ones were gone now, inside the earth and under the sea; but their dead bodies had told their secrets in dreams to the first men, who formed a cult which had never died.
The ruins of Orvhad
Within the Cavern of Black Blood lies an ancient, abandoned city, called the "City of Piled Stones."
The Island of Midnight
In the center of the cavern is a desolate island called "Midnight," which is home to a fallen temple dedicated to the Dark Gods of Corwyn.
