A tidal island lying off the northwest tip of Mainland Orkney. Rising to high cliffs in the west, it has an area of 56 ha (138 acres) and can be reached at low tide across an artificial causeway. At the foot of the slope are the remains of a settlement of early Christian and Viking times. There are interesting domestic and ecclesiastical remains here as well as fine examples of Norse hall-houses and the remains of a Cathedral and Bishop's Palace dating from the 11th century.