A souterrain, an underground passage or chamber system typically associated with early medieval settlement in Ireland, usually served purposes of storage or refuge. The one at Caherdesert takes an unusual form: rather than opening into chambers, it runs as a series of passages arranged in a zig-zag plan, with jamb stones placed at each angular bend to obstruct movement further. Whatever was being protected here, or whoever was retreating into it, was not expected to move quickly.

The site was recorded by McCarthy in 1977, drawing on local information, and it leaves no visible trace on the surface today. The pasture gives nothing away. What aerial photography has revealed, however, is that the souterrain sits within a circular enclosure, the kind of layout consistent with a cashel, a stone-walled early medieval farmstead. A standing stone, or gallán, shown on the 1936 Ordnance Survey six-inch map, stands nearby within that same enclosure. Roughly seventy metres to the north-west, there are the possible remains of a second cashel and a further souterrain, suggesting this hilltop once held more than one household, or at least more than one phase of activity. The cluster of features, none of them dramatically visible on the ground, points to a landscape that was more intensively occupied in the early medieval period than its current silence implies.