Measuring roughly eight metres north to south, less than two metres wide, and only half a metre deep, the hollow is either the collapsed remains of a souterrain or the scar left by a quarry. That ambiguity is itself revealing: a landscape feature significant enough to record, yet worn down to the point where its original purpose can no longer be confirmed.

A souterrain is an underground stone-lined passage or chamber, typically constructed during the early medieval period in Ireland, often associated with settlement enclosures and thought to have served for storage, refuge, or both. The fact that this depression sits within a cashel, a type of circular stone-walled enclosure also dating to the early medieval period, makes the souterrain interpretation plausible. Such features were commonly built inside or immediately adjacent to cashels, making use of the same stonework tradition. The site occupies the crest of a south-facing slope on a low ridge running northwest to southeast, a position that would have offered both visibility and some natural drainage, practical considerations for any early settlement. Whether the hollow was quarried to provide stone for the cashel wall itself, or whether a souterrain once ran beneath it and has since collapsed, the ground at Cloonkeen carries the faint outline of activity that is now just beyond recovery.