Hiking Croagh Patrick, near Westport, County Mayo, Ireland. Nicknamed "The Reek," the peak sits at 764 meters (2,507 ft) and is an important site of pilgrimage in County Mayo in Ireland, sitting above the villages of Murrisk and Lecanvey. It is the third highest mountain in County Mayo after Mweelrea and Nephin. It is climbed by pilgrims on Reek Sunday every year, which is the last Sunday in July. It forms the southern part of a U-shaped valley created by a glacier flowing into Clew Bay in the last Ice Age. It is now a site of Christian pilgrimage associated with Saint Patrick who fasted on the summit for 40 days in the fifth century A.D. Thousands of people climb the mountain every Reek Sunday, which is the last Sunday in July.