In a wonderful island setting, the 5th-century Celtic monastic community of Nendrum was built under the guidance of St Mochaoi (St Mahee). Its scant remains provide a clear outline of its early plan, with the foundations of a number of churches, a round tower, beehive cells, three concentric stone ramparts and a monks' cemetery. The stone sundial was reconstructed using original pieces. There's a small visitor centre.
Nendrum is 5km south of Comber, reached by a causeway and bridge.
By the bridge, look for the ruined tower of 15th-century Mahee Castle.