On it stands an enclosure, the kind of drystone boundary that in an Irish early medieval context often signals a monastic or ecclesiastical presence, demarcating sacred ground from the surrounding landscape. These enclosures, sometimes circular and sometimes irregular in plan, were a common way of defining the temenos, the set-apart space, around a church, oratory, or hermitage. On an island this remote, the presence of such a structure raises obvious questions about who built it, why they chose a place so difficult to reach, and what life within those walls might have looked like.

Caher Island has long been associated with early Christian monasticism in the west of Ireland, and it lies within a broader constellation of pilgrimage sites along this stretch of the Atlantic coast. The island is known locally as Caher or Cathair, from the Irish word for a stone fort or enclosure, which suggests that the boundary structure here was significant enough to give the place its name entirely. It sits not far from Croagh Patrick, the mountain that dominates this part of Mayo and draws its own considerable tradition of devotional practice, and the two sites are thought to have been linked within a pre-modern pilgrimage circuit. The enclosure on Caher Island is part of a small monastic complex that includes an oratory and several cross-inscribed slabs, physical traces of a community that chose isolation as a condition of spiritual life.