These underground passages, built with careful drystone construction and topped with flagstone roofing, once served as storage spaces, refuges, or ritual sites for early medieval communities. The Carnaghan souterrain consisted of two distinct chambers connected by a low, crawling passage that would have required anyone passing through to stoop or crawl on hands and knees.

The main chamber stretched 10 feet in length with a ceiling height of just 4 feet, whilst the northern chamber measured 6 feet long. This compact design was typical of souterrains throughout Ireland, where builders balanced the need for usable space with the practical constraints of construction and concealment. The discovery of an additional small passage further north in the same field suggests this area may have been home to a more extensive underground network or multiple periods of construction.

The location itself offers clues to why this spot was chosen for such a structure. Set in fertile agricultural land with a gentle slope towards the southeast, the site would have provided good drainage whilst remaining close to what was likely productive farmland. Though now sealed and inaccessible, this souterrain remains part of County Donegal's rich archaeological landscape, documented in the comprehensive 1983 Archaeological Survey that catalogued field antiquities from the Mesolithic period through to the 17th century.