The conditional phrasing matters here. A souterrain is an underground passage or chamber, typically dry-stone built, associated with early medieval ringforts and cashels across Ireland. They were used variously for storage, refuge, or ventilation, and when their roofing slabs or corbelling eventually gives way, they collapse inward and leave precisely this kind of subtle depression, a dip in the ground partly choked with rubble, easy to walk past without registering what it once was.

The cashel itself, a roughly circular enclosure defined by a stone wall rather than an earthen bank, is recorded separately. What the hollow in its north-eastern corner suggests is a subterranean element that was once integral to the settlement, a feature built and used by people whose daily lives were organised around this enclosure, probably during the early medieval period when cashels were in common use across Munster. Nothing more specific about the date or the circumstances of collapse is known from the available evidence, and the souterrain itself, if it is one, has not been excavated or formally confirmed.