About twenty metres across and defined by a fosse, a type of external ditch that typically marks the boundary of an enclosed settlement or ceremonial space, it leaves no mark on the surface of the rolling grassland. It exists, to all practical purposes, only from the air.

The enclosure came to light as a cropmark on an aerial photograph taken on 10 July 1973, part of the Cambridge University Collection of Aerial Photography. Cropmarks appear when buried features such as ditches or walls affect how vegetation grows above them; a filled-in fosse retains more moisture than the surrounding soil, producing a strip of lusher or differently coloured crop that, under the right conditions, becomes legible from altitude. The Dunmore example sits on top of a NW-SE gravel ridge, a position that would have offered its original occupants fair to good views across the valley in most directions, a consideration that recurs repeatedly in the siting of early enclosures across Ireland. A second enclosure lies roughly eighty metres to the northwest, suggesting this was not an isolated feature in the ancient landscape but part of something more organised, though the relationship between the two remains unexcavated and unexplained.

Because the enclosure is invisible at ground level, there is nothing to pick out on a walk through the area, and its precise character, whether domestic, agricultural, or otherwise, cannot be determined without further investigation. What the aerial photograph preserves is essentially a shadow, the faint outline of a boundary that someone once considered worth digging, on a ridge above a river valley, at some point deep enough in the past that the land has long since smoothed over it.