The first monastery on Inisfallen (the largest of the lake's islands) was founded by St Finian the Leper in the 7th century. The extensive ruins of a 12th-century Augustinian priory and an oratory with a carved Romanesque doorway stand on the site of St Finian's original. You can hire a motor boat with boatman (around €10) from Ross Castle for the 10-minute trip to the island. In calm weather you can hire a rowing boat (€5 per hour; allow 30 minutes each way).

Inisfallen's fame dates from the early 13th century when the Annals of Inisfallen were written here. Now in the Bodleian Library at Oxford, they remain a vital source of information on early Munster history.