Gaztelugatxe is an islet on the north coast of Spain where there is a hermitage (religious retreat) in dedication of John the Baptist. The islet is connected to the mainland with a man made walk way and stairs up to the church that dates back to the 10th century.
In the 7th season of Game of Throne the islet was used as Dragonstone with a digitally made castle on top instead of the church.