No earthwork survives above ground, no bank, no ditch, no suggestion of the circular enclosure that once occupied a north-facing slope above the villages of Donnybrook and Douglas. It has been levelled entirely, leaving only a cartographic ghost and, somewhere beneath the soil, a souterrain.

The 1842 Ordnance Survey six-inch map recorded the fort as a semicircular arc, its southern edge meeting a trackway running northeast to southwest. That partial arc suggests the western or eastern half of the enclosure had already been lost by the time the surveyors came through, or that the trackway itself had long since eaten into it. Ringforts, known in Irish as raths, are the most common archaeological monument type in Ireland, typically the enclosed farmsteads of early medieval families, dating broadly from the sixth to the twelfth centuries. Most survive as low earthen banks and ditches, sometimes with an internal souterrain, an underground stone-lined passage used for cool storage or as a place of refuge. The Castletreasure example retains that underground element, recorded separately and still present beneath the levelled surface, even as everything above ground has gone.

What makes the site quietly odd is its setting. It sits within a domestic garden, overlooking what are now suburban Cork neighbourhoods, and it registers as nothing to the eye. The map evidence and the subsurface souterrain are the only remaining indicators that this slope was once, for someone, a place of deliberate enclosure and daily life.