A souterrain is an underground passage or chamber, typically stone-lined, built during the early medieval period in association with ringforts and used variously for storage, refuge, or ventilation of adjacent structures. At Ballynahowna, one such feature was associated with a rath, the Irish term for a ringfort, a circular enclosure defined by earthen banks that served as a farmstead for a family of some local standing. But whatever once lay beneath the soil here, none of it is now visible at ground level.

The site carries a certain archival peculiarity alongside its physical absence. It does not appear on any edition of the Ordnance Survey six-inch maps, the standard cartographic record that captured so much of the Irish landscape from the nineteenth century onwards. Its existence was nonetheless formally acknowledged when it was included in the Record of Monuments and Places in 1995, the statutory list that affords legal protection to archaeological sites across the country. That recognition came without anything to see, which places Ballynahowna in an odd category: a protected site defined entirely by what is no longer apparent, recorded because the evidence for something once being there was convincing enough, even if that evidence has since been swallowed by soil, subsidence, or time.