Of the forty-six islands scattered across the lough, Saint’s Island stands out as the likely site of this original monastery, which later became a priory under the Augustinian Abbey of SS Peter and Paul in Armagh during the 1130s. The monastery’s primary role was serving pilgrims visiting St. Patrick’s Purgatory, a cave that drew visitors from across medieval Europe and inspired a substantial body of literature. Though some sources suggest the cave was originally on Saint’s Island before the pilgrimage relocated to nearby Station Island, the monastery continued its ministry until abandonment in the late sixteenth century.

Today, Saint’s Island reveals fascinating archaeological remains that hint at its religious past. The western half of an earthen enclosure, roughly 20 metres across with an external fosse, marks the oldest visible structure. A rectangular graveyard measuring 27 by 22.5 metres, enclosed by drystone walls, dominates the central area with rubble piles and displaced graveslabs suggesting centuries of burials. A 44-metre pathway defined by two lines of grass-covered stones connects this cemetery to the foundations of another rectangular building, possibly a church or dwelling, measuring 9 by 6.55 metres with walls nearly a metre high. Additional features include what appears to be a partial circular enclosure to the northeast, various earthen banks indicating old field boundaries, and remnants of a quay at the island’s northeast end where pilgrims once landed.

The pilgrimage route itself tells a story of medieval devotion, with an ancient roadway from Pettigo village passing significant sites like Rathnacross ringfort and Templecarn church before reaching the southwest shore of the lough. Here, a wooden bridge once connected the mainland to Saint’s Island, with natural boulders still visible in the water possibly marking its supports. Other religious landmarks dot the landscape: St. Brigid’s Chair, a natural L-shaped stone on the southeast shore, and St. Dabheoc’s Seat, formerly a stone seat before a grave-like opening on a southern hill, though forestry has now obscured this site. These scattered monuments create a sacred geography that sustained one of Ireland’s most enduring pilgrimage traditions.