Reek Sunday (Irish: Domhnach na Cruaiche), Garland Sunday or Crom Dubh Sunday (Irish: Domhnach Crom Dubh) is an annual day of pilgrimage in Ireland.

On the last Sunday in July, thousands of pilgrims climb Ireland's holiest mountain, Croagh Patrick (764 metres) in County Mayo. It is held in honour of Saint Patrick who is said to have spent forty days fasting on the mountain in the 5th century. Masses are held at the summit, where there is a small chapel. Some climb the mountain barefoot, as an act of penance, and some carry out 'rounding rituals', which were formerly a key part of the pilgrimage. This involves praying while walking sunwise around features on the mountain: seven times around the cairn of Leacht Benáin (Benan's grave), fifteen times around the circular perimeter of the summit, seven times around Leaba Phádraig (Patrick's bed), and then seven times around three ancient burial cairns known as Reilig Mhuire (Mary's cemetery). Until 1970, it was traditional for pilgrims to climb the mountain after sunset