On which island on Lough Derg Lake is the "Purgatory of Saint Patrick" located?

St Patrick's Purgatory is an ancient pilgrimage site on Station Island in Lough Derg, County Donegal, Ireland. According to legend, the site dates from the fifth century, when Christ showed Saint Patrick a cave, sometimes referred to as a pit or a well, on Station Island that was an entrance to Purgatory.