The enclosure stretches roughly 112 metres east to west and 95 metres north to south, a substantial footprint defined by an inner bank, an intervening fosse (a ditch cut as part of a defensive or boundary arrangement), and an outer bank. The outer bank, at up to 1.3 metres high, is the most legible feature today, having been absorbed into a modern field boundary that has at least kept it from disappearing entirely. The inner bank has fared less well: it survives in most places as a low, worn scarp barely 0.3 metres high, and on the northern to north-eastern arc someone made a deliberate attempt to level it. A disused silage pit occupies the western side, and a modern causeway crosses the fosse at the west-north-west.

What makes the site genuinely difficult to read is the combination of features it contains. Within the north-eastern quadrant of the interior sits a cillin or children's burial ground, and a probable souterrain, an underground stone-lined passage typically associated with early medieval settlement or ecclesiastical sites, has also been identified in association with the enclosure. The presence of both could point toward an early Christian foundation. Yet the scale of the enclosure and its prominent, slightly elevated position relative to the bog suggest something older, possibly prehistoric, in origin. It is not unusual for early medieval communities to have reused and reinterpreted prehistoric earthworks, layering new meanings onto older ground, and Cloonagh may be a case of exactly that kind of long, complicated occupation. The site was noted by Neary in 1914, placing it within a tradition of antiquarian observation that recognised its strangeness even then.