The Call of Cthulhu by H. P. Lovecraft audiobook.
The worshipers of this ancient tentacled horror are still with us, waiting for this terrible being to awake and take vengeance again on an earth filled with nonbelievers. Lovecraft delves into this eons old cult in the greatest detail of any of his stories about Cthulhu and gives us hints about how it is worshiped and the abominable rituals involved. Creepy. Very creepy.