Saint’s Island, formerly known as St. Dabheog’s Island, holds the remnants of a monastic settlement traditionally believed to have been founded by St. Patrick himself in the fifth century. The saint reportedly installed Dabheoc as the first abbot here, establishing what would become a crucial religious centre. By the 1130s, the monastery had transformed into an Augustinian priory dependent on the Abbey of SS Peter and Paul in Armagh, though it was eventually suppressed and abandoned towards the end of the sixteenth century.

The island’s archaeological remains tell a complex story of religious life and pilgrimage. Visitors can still trace the western half of an earthen enclosure, roughly 20 metres in diameter, complete with an outer fosse. A rectangular graveyard, enclosed by drystone walls and measuring 27 by 22.5 metres, dominates the eastern portion where the original enclosure was destroyed. At its centre, a jumbled pile of rubble holds graveslabs placed without apparent order. A 44-metre pathway, marked by two lines of grass-covered stones, leads northeast to the foundations of another rectangular structure, its drystone walls still standing up to 95 centimetres high. Additional features include what appears to be a partial circular enclosure, various earthen banks suggesting old field boundaries, and evidence of an ancient quay at the island’s northeast end.

The monastery’s primary purpose was to serve pilgrims journeying to St. Patrick’s Purgatory, a cave that drew visitors from across medieval Europe and inspired a substantial body of literature. Whilst the purgatory is now associated with nearby Station Island, some sources suggest it originally stood on Saint’s Island itself before being relocated. The ancient pilgrimage route from Pettigo village can still be traced past Rathnacross ringfort and Templecarn church, leading to the southwest shore where a wooden bridge once connected the mainland to this sacred island. Natural boulders projecting from the lake may be all that remains of the bridge supports, whilst other pilgrimage sites around the lough, including St. Brigid’s Chair and St. Dabheoc’s Seat, have either survived as natural features or disappeared beneath modern forestry.