Santuario protohistórico de Gastiburu Historical milestone · Arratzu, Gernika-Bermeo, Bizkaia Iron Age site (around the 3rd century BC) located on Mount Gastiburu, within the territory of Arratzu. It is one of the documented protohistoric sanctuaries in Bizkaia, with archaeological evidence of ritual activity predating Romanization. siglo III a.C. Photo: Txo (CC BY-SA 4.0) What to see and do in Arratzu