Station Island in Lough Derg in County Donegal has been used as a pilgrimage site for Christians since the middle ages. The island is the alleged site of a dark cave where St. Patrick spent a number of days in fasting and meditation, and where he observed the cleansing of sins from souls in the fires of Purgatory.
Today, people come from all over the world for a 3 day pilgrimage of prayer and fasting to rid themselves of their sins. Participants take a boat to the island, then walk barefoot around the “beds” (various monuments) of the saints while repeating a mantra-like prayer. Fasting for three days with one meagre meal of toast and tea per day and staying awake for an entire night’s vigil are parts of the experience. Station Island is open for the 3-day retreat from June 1 to the feast of the Assumption on August 15. The pilgrimage attracts over 13,000 participants annually.
There is a description of an early 19th century pilgrimage to Lough Derg in my novel, “Donegal Generations.”