A cairn, in the Irish prehistoric context, is typically a mound of stones raised over a burial or as a territorial or ceremonial marker, and this one on Knocknadobar is modest by any measure: roughly six metres across in both directions and standing just a metre above the surrounding ground. What it lacks in scale it compensates for in placement, set at a point from which the Ferta river valley spreads out below in considerable breadth.

The cairn is composed mainly of small, irregular stones, and there is visible collapse at its southern and north-eastern sides, the kind of quiet deterioration that accumulates over centuries of exposure at altitude. No excavation record appears to accompany the site, so its precise age and purpose remain unconfirmed, though cairns of this type on Irish mountain summits are generally associated with prehistoric activity, sometimes Bronze Age. The Iveragh Peninsula is dense with such remains, many of them catalogued through fieldwork carried out in the early 1990s and published in 1996 by A. O'Sullivan and J. Sheehan in their archaeological survey of south Kerry.