That uncertainty is itself part of what makes this site worth knowing about. A souterrain, for those unfamiliar with the term, is a man-made underground structure, typically stone-lined, associated with early medieval settlement in Ireland and used variously for storage, refuge, or concealment. The one recorded at Ballinlyna sits in pasture just west of the townland boundary with Ballyroe, and its current condition is, to put it plainly, unknown.

The site has a quietly puzzling cartographic history. It does not appear at all on the Ordnance Survey's six-inch map from 1840, nor on the more detailed twenty-five-inch edition published in 1897, suggesting it either went unnoticed by surveyors or had already lost any obvious surface expression by those dates. It surfaces, so to speak, only on the later Cassini edition of the OSi six-inch map, where it is marked with the annotation 'Souterrain' and shown as a small circular opening just west of a stream. That stream, like the souterrain itself, has since disappeared from view. Aerial imagery captured between 2011 and 2013 via Digital Globe, and corroborated by Google Earth orthoimages, shows no surface remains of either the souterrain or any watercourse in the area. The record was compiled by Fiona Rooney and uploaded in November 2021.

For anyone inclined to visit, the site lies in agricultural pasture, and access would require landowner permission. The ground gives nothing away visually, and there is no marker, no signage, and no obvious feature to locate. The interest here is less in what can be seen and more in what the cartographic record implies: something was identified at this spot at some point between the nineteenth-century surveys and the Cassini revision, noticed, named, and then effectively swallowed by the landscape. Whether the structure below ground remains intact, has collapsed, or was always more modest than the label suggests, no surface investigation has so far resolved.