Lough Derg (St Patrick's Purgatory)
County Donegal, Ireland
An island in Lough Derg said to contain a cave leading directly to Purgatory — revealed to Saint Patrick so he could show doubters what awaited sinners. Medieval pilgrims came from across Europe to descend into it. The penitential tradition continues to this day: three days without sleep, barefoot on the cold stone island.
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