Look more closely, though, and the island reveals itself to be a crannóg, an artificial or artificially enhanced island of the kind built and inhabited across Ireland and Scotland during the early medieval period, typically constructed from layers of stone, timber, and organic material to create a defensible dwelling place in open water. What distinguishes this particular example is the scale of what was built around it: three causeways of large limestone blocks radiate outward from its shores, the longest running fifty-eight metres from the southeast shore towards the neighbouring Turgesius Island, five to six metres wide, and composed of stones up to a metre in length.

The island is oval in plan, measuring roughly thirty metres northeast to southwest and sixty metres northwest to southeast, and rises about four metres above the lake surface. Beneath the trees and overgrowth, it is essentially a large cairn of medium to large limestone blocks, with a stone kerb of larger slabs running along the east shore. Archaeologist Aidan O'Sullivan, writing in 2004, concluded that the island is partly natural in origin but was likely enhanced and kerbed during the early medieval period. Its name gestures towards a possible ecclesiastical connection, suggesting at some point a religious community of women may have had a presence here. The lake holds two further crannógs within close range, Castle Island to the south-southwest and Turgesius Island to the southeast, and all three share a strand of local folklore linking them to Viking activity, a reminder of how thoroughly the Norse presence embedded itself in the memory of the Irish midlands long after the longships had gone.