Nendrum is a fifth century Monastery, now only ruins, on Mahee Island in County Down, Northern Ireland. The ruins include old walls, graves, the stump of a round tower and of a church with its sundial. It was founded by Mochaoi and was probably pillaged and destroyed in a raid by the Danes in the tenth century. The stump of the round tower is in the background and the ruins of the church with its sundial are in the foreground. Mahee Island, the site of the monastery, is on the west side of Strangford Lough in County Down, Northern Ireland and is reached by a narrow causeway that passes the ruins of Mahee Castle.