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Photo: Daviddphotos, CC BY-SA 4.0 via Wikimedia Commons
The first monastery was founded in the 6th century, but the ruins you see now are of the Franciscan friary of 1448. (Actually not an abbey, where monks live in seclusion: friars preached in their locality.) It was smashed up on several occasions before Dissolution and a final scourging by Cromwell. The ruin is roofless but extensive; a striking central courtyard has a yew tree and cloisters. The graveyard remains in use.
Muckross Abbey is a ruined Franciscan friary located in the Killarney National Park, County Kerry, Ireland. Previously known as the "Friary of Irrelagh", the abbey was founded in 1448 for the Observantine Franciscans by Donal McCarthy Mor. Today the abbey is largely roofless, but retains most of its original walls.
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This now hosts the park visitor centre. It was originally a grand 18th-century chateau but proved serially combustible, so eventually the owners gave up and decamped to the stables, converting them into the present house.