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. With another small neighboring island, Aketx, they form a protected biotope that extends from the town of Bakio until Cape Matxitxako, on the Bay of Biscay.