What makes it quietly odd is not its size or its name, but a detail buried in an Ordnance Survey map from 1838: at the time of that survey, the spot where the cairn sits was surrounded by water, making it a true island. Today it sits on dry land, the lough having retreated or the ground having shifted enough over the intervening decades to leave it stranded on a headland with the Aille River running along its eastern edge.

The cairn itself appears to be artificially constructed rather than a natural accumulation of glacial debris, which places it in a long tradition of deliberate stone-built monuments in the west of Ireland, though precisely when it was raised and by whom remains unrecorded. A large tree now grows from its interior, its roots threading through the stonework. The name, Priest Island, hints at some association with early Christian hermitage or ecclesiastical use, a pattern common in the lake districts of Mayo and Galway, where small islands and islets were favoured as places of retreat or burial. Whether this particular spot ever held a cell, a grave, or simply acquired its name through local tradition is not documented.