In the middle of the lough is an islet known as Station Island or, more popularly, St. Patrick's Purgatory, which has been a place of pilgrimage, since at least the 12th century and possibly from the sixth century, and remains very busy to this day. Here, pilgrims fast (being allowed only one meal a day, of black tea or coffee and dry toast) and make barefoot circuits around the stone remains of monks cells during their 3-day pilgrimage. During the first night they must keep a vigil, staying up all night and continuing prayer. The traditional three-day pilgrimage runs from June 1 until August 15th every year. The church on the island is St. Patrick's Basilica.
Station Island is the title of the long and epic poem written by Séamus Heaney. It is also the scene of "The Pilgrimage to Lough Derg" by the Irish writer William Carleton. His experience there led him to abandon thoughts of becoming a Roman Catholic priest, and he converted to the Church of Ireland.