Gaztelugatxe is an islet on the coast of Biscay belonging to the municipality of Bermeo, Basque Country (Spain). It is connected to the mainland by a man-made bridge. On top of the island stands a hermitage (named Gaztelugatxeko Doniene in Basque; San Juan de Gaztelugatxe in Spanish), dedicated to John the Baptist, that dates from the 10th century, although discoveries indicate that the date might be the 9th century.