The name is apt. This is not a dramatic hilltop fortification but something quieter and more domestic, a ringfort tucked into the landscape as if it had simply grown there. Ringforts, known in Irish as raths or liosanna, were the typical enclosed farmsteads of early medieval Ireland, generally dating from roughly the fifth to the twelfth centuries. Thousands survive across the country, though many are only legible to those who know what to look for.

Coolbeg is a univallate example, meaning it has a single enclosing bank rather than the multiple concentric rings that mark higher-status sites. The bank, built from earth and stone, rises about 1.1 metres above the outer fosse, which is a shallow ditch that once helped define and defend the boundary of the settlement. The fosse runs around most of the circuit, though it is interrupted to the east where a later field boundary cuts across it, the kind of incremental damage that agricultural land use accumulates over centuries. The interior measures roughly 24 metres across and sits at much the same level as the surrounding ground, which is itself slightly unusual. Several breaks exist in the bank, the largest on the north-east side at around 3 metres wide, possibly indicating an original entrance. More intriguing are two rectangular discolourations visible in the grass of the northern interior. These patches, which show up differently from the surrounding turf, may mark the footprints of early structures, the ghostly outlines of buildings whose walls have long since dissolved back into the earth.