The structure was identified not by ground survey but from an aerial photograph, and what that photograph revealed was a D-shaped enclosure where a circle ought to be, the missing northwestern half apparently swallowed by a later field wall that now runs straight across what would have been the interior.

Ringforts, also known as raths or cashels depending on whether they were built from earth or stone, were the most common form of rural settlement in early medieval Ireland, typically enclosing a farmstead and its immediate household. The Coolnaha example is stone-built, the curving bank surviving to a width of roughly two to two and a half metres and standing only about half a metre high on the exterior at its best-preserved eastern stretch, where it blends into low rises of earth and stone with loose field clearance material mixed in. The northern and northeastern sections have been reduced to little more than a slight undulation in the ground. There are two narrow breaks on the southeastern to southern arc, each around three metres wide, and a larger gap of over seven metres at the south-southwest, which may indicate an original entrance or simply centuries of collapse and robbing. Inside, the ground is grassy and slopes gently down toward the southeast; faint traces of cultivation ridges run on a northeast-southwest axis, and a low, partly sod-covered heap of field stones sits slightly southeast of centre. Those same ridge patterns continue into the surrounding fields to the north and east, suggesting the enclosure was eventually folded into the working agricultural landscape around it rather than left deliberately apart from it. The northwestern half of the original circle, if it ever survived above ground, has left no visible trace on the far side of the field wall that now bisects the site.