The depression measures roughly 1.3 metres north to south and 0.4 metres east to west, sinking to a depth of around 0.2 metres. Unremarkable on the surface, it is the kind of subtle subsidence that archaeologists read as a warning sign: a collapsed souterrain chamber lying just beneath.

A souterrain is an underground passage or chamber, typically built of dry stone, that was constructed in association with early medieval settlements in Ireland. They were used for storage, refuge, or both, and are frequently found within or close to ringforts, the circular earthwork enclosures that served as farmsteads from roughly the fifth to the twelfth century. The feature at Condonstown may well be the same souterrain recorded by Power in 1917, who noted it in what he described as a lios, the Irish word for such an enclosure, on Lord Barrymore's farm. That connection across more than a century of references is itself quietly telling: the site was noticed, noted, partially identified, and then left largely undisturbed, its underground structure slowly pressing itself upward through the turf as a shallow hollow.