The structure measures just 7.4 metres across, with a southwest-facing entrance roughly 1.8 metres wide, and the interior tilts gently downward toward the south. Loose stones scattered on the downslope outside the wall suggest the collapse happened gradually, over a long stretch of neglect rather than any single event.

Enclosures of this kind, built from drystone, which is stone laid without mortar, are found throughout the Irish uplands and can date to anywhere from the early medieval period onward. They were used variously as animal enclosures, small settlement boundaries, or as part of a wider pattern of agricultural organisation on marginal land. At Derreenacullig, the wider context supports that agricultural reading: a relict field wall survives roughly 18 metres to the south, hinting at a landscape that was once more deliberately managed than its current rough, commonage state would suggest. A small stream lies about 14 metres to the west, close enough to have been practical for anyone living or working within the enclosure. Together these features, the wall, the stream, the entrance oriented away from the prevailing Atlantic weather, point to a place that was once carefully chosen rather than casually occupied.