The ruins of the monastery founded in the 7C and later pillaged by the Vikings in the 9 and 10C, are surprisingly extensive. They are made up of Glebe House, built in the 15C whose two storeys were most probably the abbot's abode, a round tower with a conical roof (11 or 12C) which served as a lookout and refuge against enemy attacks, a 13C cathedral and several 11-12C churches.