The only evidence that it exists at all is a single aerial photograph, taken in 1971, which caught the crop growing above it behaving differently from everything around it.

The photograph, catalogued as FSI 206/5/4, revealed a cropmark, the faint but telling discolouration that appears in fields when buried features affect how plants grow above them, drawing moisture or nutrients differently depending on whether the ground beneath has been disturbed by a ditch, a wall, or a foundation. What it showed at Cappagh was an elongated oval enclosure, oriented roughly northeast to southwest, measuring an estimated 34 metres along that axis and around 22 metres across. The record was compiled by archaeologist Geraldine Stout and uploaded to the national survey in August 2011. No excavation is noted, and no surface trace remains. The enclosure sits on fairly level ground to the north of a local stream, in the kind of unremarkable agricultural setting where early medieval ringforts, settlement enclosures, and similar features are often quietly buried.

There is, practically speaking, nothing to see here in the conventional sense. The site sits in rough pasture, and without the benefit of the right crop, the right season, and an aircraft overhead, the enclosure gives nothing away. That is, in its own way, the point. For anyone interested in how archaeology works as a discipline, Cappagh is a useful reminder that the record of human settlement in Ireland is full of features known only from above, catalogued on the basis of a single good photograph taken decades ago, and otherwise entirely concealed. The area around Cappagh is accessible enough to visit if you are oriented by the relevant Ordnance Survey mapping, but expect level ground, rough grass, and no visible feature whatsoever. The site is the kind of entry that rewards curiosity about the nature of archaeological evidence rather than about monuments you can actually touch or photograph.