Others exist only as pale shadows in a farmer's field, legible solely from the air and only under the right conditions. The circular enclosure at Ballynamona in County Cork belongs to the second category. Its fosse, a defensive or boundary ditch that would once have defined the perimeter of the enclosure, survives as a cropmark, a faint discolouration in growing crops caused by the buried ditch retaining more moisture than the surrounding soil. The enclosure measures roughly 25 metres in diameter, and it is visible only in aerial photography rather than from ground level.

The cropmark was captured in a July 1989 aerial survey, and it is not an isolated find. Roughly 40 metres to the east-north-east lies a ring-ditch, a related class of circular feature often associated with prehistoric funerary or ceremonial activity. About 150 metres to the north-north-east sits a ringfort, the type of enclosed farmstead that was widespread in early medieval Ireland, typically dating from somewhere between the sixth and tenth centuries. Whether all three features are broadly contemporary is not certain, but their proximity suggests this corner of North Cork was a focus of settlement or activity across more than one period. Additional linear cropmarks in the same field may represent the buried remnants of field boundaries, levelled long ago and now invisible except from altitude.