Built by Norman knight John de Courcy for the Cistercians in 1180 on an earlier Irish monastic site, Inch Abbey is visible across the river from Down Cathedral – and yes, it's another Game of Thrones filming location. Most of the ruins are just foundations and low walls; the atmospheric setting beside the marshes of the River Quoile is its most attractive feature.
Inch Abbey is off the A7 Belfast Rd just across the river, north of Downpatrick.
John de Courcy commissioned one of the monks at Inch Abbey to rewrite the legends of St Patrick; it's possible that the story of St Patrick banishing the snakes from Ireland was written here.