What makes it more than an ordinary islet is what lies on and beneath its vegetation: the footprint of a cashel, a type of stone-walled ringfort, built onto a wide stone platform that effectively defines the island's shape. It is, in miniature, a constructed place as much as a natural one.

Known as Man's Island, the site is subcircular in plan and encloses an earthen flat-topped mound, the kind of raised interior typical of ringfort construction, where the enclosed ground was built up and levelled for habitation or storage. Traces of a retaining wall survive on the western side of the mound, suggesting the original structure was more substantial than what remains today. Particularly telling is the stone-lined quay visible on the eastern shore of the island, a detail that points to deliberate, purposeful use of the water around it. Cashels of this kind, dry-stone enclosures usually associated with early medieval settlement in Ireland, are common on land across Connacht, but finding one positioned on a lake island, with its own landing point, speaks to a community that organised itself around the water rather than simply beside it.