The Leviathan altar.
The Leviathan altar was a stone construction used by the Leviathans for ceremonies. Two sliding slabs made the altar, situated in front of a large carving of the Naga, or symbol of the Leviathan people. When the slabs moved apart, a small cave-like entrance could be exposed beneath the Naga symbol. This led to an underground area of the altar.
Barnabas Collins first encountered the altar in 1796 while travelling the path between Collinwood and the Old House. He realized that he could no longer find his way and that he had become lost in a mist that surrounded the altar. Two Leviathans, Oberon and Haza, appeared, intercepting Barnabas and preventing him from continuing. They performed a ceremony over Barnabas that seemed, at first, to rid him of his conscience and will (886, 887). Later, it was revealed that this ceremony placed the subconscious fear of the return of the vampire curse and the death of Josette Collins into Barnabas' mind (938). The Leviathans prepared Barnabas to travel back to 1969 as the leader of the cult until the essence of their new leader had fully grown (887). The altar travelled to 1969 before Barnabas returned, appearing very near to Paul Stoddard in the woods near Collinwood (887).
Carolyn Stoddard found the altar in the woods and wondered about its origins. Later that night, the altar opened, sliding to the sides of the Naga carving (888), and Barnabas Collins returned to 1969 (889).
Barnabas took Philip Todd to the altar to punish him when he did not follow orders unquestioningly (894/895). David Collins entered the altar and fell under Leviathan control soon after (896).
Once free of Leviathan control, Barnabas took the Naga Box to the altar and attempted to destroy it, but instead found a bat that had been placed inside the box by Jeb Hawkes (950). Once attacked, Barnabas became a vampire once more (951).
Nicholas Blair attempted to force Jeb and Carolyn Stoddard into performing the ceremony that would transform Carolyn into a Leviathan, but Jeb smashed the Naga Box, causing the altar to explode (965).