What was once a cashel, a type of ringfort defined by a stone wall rather than an earthen bank, now survives mainly as a line of collapsed drystone masonry tracing an irregular circuit across the rough pastureland. Measuring approximately 38 metres east to west and 31 metres north to south, it is a substantial structure in theory, though vegetation has done considerable work against it. From the south and south-east, dense overgrowth has obscured the wall almost entirely, giving the site the quality of something that is easier to sense than to see.

Cashels of this kind were typically built during the early medieval period in Ireland, serving as enclosed farmsteads for a single family or small community, the stone wall performing the same function as the raised earthen banks of the more common earthwork ringforts found elsewhere in the country. The presence of a possible souterrain, an underground passage or chamber usually associated with storage or refuge, suggests the site was once a functioning domestic settlement of some complexity. Souterrains are frequently discovered in association with cashels across the west of Ireland, often only partially investigated or identified from surface anomalies. Whether the one at Polldonoghoe was ever properly explored is unclear, but its suspected presence adds a subterranean dimension to what might otherwise appear to be simply a tumbled ring of stones on a hillside.