A souterrain is an underground stone-lined passage or chamber, typically constructed during the early medieval period in Ireland, and built for purposes that archaeologists still debate, variously proposed as refuges, storage spaces for dairy produce, or places of concealment in times of raiding. Their presence in a landscape is easy to overlook; from the surface, there may be nothing visible at all, or only a slight hollow where the ground has settled over centuries of slow collapse.

The placename Cill Ón Chatha carries its own quiet weight. The element "cill" points to an early ecclesiastical site, a cell or church, suggesting that this corner of south-west Kerry was once a place of some religious significance in the early Christian centuries. Souterrains are frequently found in association with ringforts and early monastic enclosures, so the pairing of underground structure and ecclesiastical placename here fits a pattern well known across Munster, even if the specific details of this example remain sparse in the published record.