In the 1840s, surveyors working on the Ordnance Survey Name Books recorded it as 'very large' and 'double ringed', a description that now requires some imagination to verify. A ringfort, or rath, is an enclosed farmstead of the early medieval period, typically defined by one or more circular earthen banks and ditches; the double-ringed variety would have signalled a household of some status. What remains at Lisnagrave is a single circular enclosure roughly 30 metres across, its inner bank worn low and its interior now crowded with coniferous trees.

The reason the site looks so diminished is not simply the passage of time. According to local knowledge, the outer bank and the fosse, the ditch that separated it from the inner ring, were removed during the 1980s, most likely in the course of agricultural improvement. The outer bank had stood around two metres high and the fosse was a metre and a half deep, features substantial enough to have made the site genuinely imposing. What survives of the inner bank is modest by comparison, rising barely half a metre above the surrounding ground on its exterior face. Beneath the interior, however, there is a souterrain, an underground stone-lined passage of the kind often associated with early medieval settlement, used variously for storage, refuge, or concealment. Around 80 metres to the south-east, a stone row adds another layer of prehistory to the immediate landscape, suggesting that this ridge was a place of significance across several different periods.