A subcircular depression in the stone, roughly three metres across and half a metre deep, with rubble gathered along its southern edge, might be a natural hollow in the karst limestone beneath. It might be a cave. Or it might be a souterrain, an underground passage of the kind early medieval Irish communities built beneath their settlements for storage or refuge. The ambiguity is part of what makes this quietly anomalous site worth attention.

The structure is a cashel, a type of ringfort built from stone rather than earthen banks, set into the south-west-facing slope of a low knoll in the mixed karst and pasture landscape of Rinnamona. Its interior diameter runs to roughly 24 metres on a north-west to south-east axis, and what remains of its defining wall is double-faced, meaning it was built with a deliberate inner and outer skin of stone, the kind of construction that signals some degree of organisation and intent. The wall survives in reasonable form along the north-east to south arc, where it stands up to about 0.8 metres on its exterior face, with moss-covered collapsed sections adding a combined width of around four metres. Elsewhere it has been robbed out entirely, its line taken over by later drystone field walls that follow roughly the same curve, a common fate for early medieval structures in farming landscapes where stone was a useful resource. The site appeared on the first Ordnance Survey six-inch map in 1842 and again on the Cassini edition of 1920, marked with hachuring that indicated an enclosure of some kind, though by 1996 it was catalogued simply as an Enclosure rather than given a more specific classification. A second enclosure lies approximately 65 metres to the south-west, suggesting this part of Rinnamona was once more substantially occupied or organised than the current pastoral quiet would imply.