Duncannon Fort

This Cistercian abbey was founded in 1200 by the Earl of Pembroke, who'd vowed to do so if the heavens preserved him when his ship was caught in a storm. It was populated by monks from Tintern Abbey in Wales, which by way of disambiguation was dubbed Tintern Major while the new abbey was Tintern de Voto — "of the Vow". It was dissolved in 1539 and the lands passed to the Colclough family until the 20th century. It's a substantial ruin with nave, chancel, tower, chapel and cloister, set in wooded parkland with walking trails.

There's been a beacon here since the 5th century, and the tower was completed by 1240, so it's among the world's oldest lighthouses. It's a 35-m-high with four storeys: in the top chamber monks tended the beacon fire and later the lantern. Secular lighthouse keepers took over from the 17th century, until it was automated in 1996.