In his discussion of the role ghosts play in Shakespeare’s plays, Stephen Greenblatt makes a digression into Catholic and Protestant perspectives on the afterlife. Here is an amusing little gem concerning Purgatory.
“Purgatory was a vast prison house under the earth where souls would suffer torments until they had paid for the sins they had committed during life. (Some thought there was an entry to it in Ireland, through a cave in the county of Donegal discovered by Saint Patrick.)”