Dún Dúchathair or simply Dúchathair (anglicized Doocaher), meaning "black stone ringfort", is a large stone fort on Inishmore (one of the Aran Islands) in County Galway, Ireland. Due to erosion, it now sits on a rocky promontory that stretches out into the sea. On its outer side there are large walls, reaching 6 metres high and 5 metres wide. On the inside are the ruins of various rooms, possibly "beehive" huts. There is also evidence of a cheval de frise protecting the entrance.