Beneath it, or rather framed by it, lies the entrance to a souterrain, an underground passage or chamber of the kind commonly built in early medieval Ireland for storage, refuge, or both. The building itself is modest by any measure: when the antiquarian H. Knox described it in 1911, he recorded foundations roughly twenty-two feet square, a footprint barely large enough for a single room. A later survey in 1990 placed it more precisely, noting a structure measuring 3.1 metres north to south and 2.8 metres east to west, defined by a low earthen bank no more than thirty centimetres high.

A rath, also known as a ringfort, is a roughly circular enclosure defined by an earthen bank and ditch, and represents one of the most common monument types surviving across the Irish countryside, most dating to the early medieval period. What makes this particular example at Ballymartin quietly unusual is the density of occupation within it. The western half contains this house and its souterrain, while a second house sits in the northern half of the same enclosure. The picture that emerges is of a fairly organised domestic arrangement within a single defended space, though when exactly people lived here, and for how long, remains unresolved. Knox's account from over a century ago and the 1990 fieldwork by Lavelle between them offer only outlines, not answers.