A souterrain is an underground stone-lined passage, typically associated with early medieval ringforts and cashels, a cashel being a stone-walled enclosure of the same period. Their purposes are debated, but storage and refuge are the most commonly proposed uses. What makes this particular site quietly odd is the layering: a natural passage in the rock, and then a constructed underground passage built directly against its mouth, as though one subterranean space demanded another.

The cave itself is a low, tight corridor, described by the researcher Self in 1980 as running approximately 19 metres in length, just half a metre wide and a metre high. That is a passage you would need to crawl through rather than walk, and one that offers little comfort at either end. It appears on both the 1840 and 1916 editions of the Ordnance Survey six-inch map simply as "Cave", suggesting it was a recognised feature of the local landscape across at least two generations of mapping. Whether the people who built the cashel and its souterrain were making use of the cave for practical reasons, integrating a natural feature into their defensive or storage arrangements, or whether the relationship was more incidental, is not recorded.