The site reveals itself only from the air, and only under the right conditions: a cropmark, the faint differential growth of plants over buried soil disturbances, tracing out a curvilinear enclosure roughly 35 metres in diameter. Cropmarks appear when the buried remains of a fosse, the ditch that once defined such an enclosure, retain more moisture than the surrounding subsoil, causing the vegetation above to grow slightly taller or greener, a ghost of the original structure visible only in aerial photography.

The enclosure at Raheennagun was identified in exactly this way, picked out on an aerial photograph taken on 16 July 1990. The cropmark outlines a roughly circular form defined by a fosse, with an entrance oriented to the south-east. A spring was recorded immediately to the south-south-west of the enclosure on the first edition Ordnance Survey six-inch map of 1839, the area around it noted as tillage, suggesting the land had been worked for generations without anyone necessarily knowing what lay beneath. The proximity of a spring is unlikely to be coincidental; water sources were consistently significant in the siting of early enclosures in Ireland, whether for practical or ritual reasons. About 110 metres to the west sits a ringfort, a type of enclosed farmstead common across early medieval Ireland, typically formed by one or more earthen banks and ditches surrounding a domestic space. The two features may be unrelated, or they may reflect a longer pattern of settled activity in this small area of Kilkenny, a clustering that is not unusual but is no less interesting for that.