The problem is that nobody can see it any more. A cashel is a stone-walled ringfort, a form of early medieval enclosure common across Ireland, and a souterrain is an underground stone-lined passage or chamber, typically associated with such sites and thought to have served for storage, refuge, or both. This particular one was recorded on the 1933 edition of the Ordnance Survey six-inch map, plotted neatly at the centre of the cashel, which gives it a kind of cartographic afterlife even as the physical reality has become inaccessible. The interior of the cashel is now very heavily overgrown, and no visible surface trace of the souterrain survives.

What the 1933 map captures is itself already a moment of recording rather than discovery. By that point, Irish antiquarians and surveyors had long been noting such features across the landscape, even when local knowledge of them was fading. The souterrain at Carrigeen exists now mainly as a mark on ageing paper, its relationship to the cashel that once enclosed it reduced to a dot and a label. Whether the passage beneath the ground remains structurally intact, collapsed, or entirely silted over is unknown.