This subcircular enclosure presents something of an archaeological puzzle; it could be either a bivallate site with two defensive rings, or a univallate enclosure containing an internal structure. The outer boundary is marked on its northern side by a grassed bank standing up to one metre high, where stones peek through the earth covering, whilst the southern edge is defined by a sharp change in ground level, reinforced with large stones. A stream meanders alongside the northern bank, perhaps originally chosen for its strategic water supply.

Within this outer perimeter, set back between two and ten metres, sits an oval inner enclosure measuring approximately 25 metres east to west and 15 metres north to south. Its boundaries are traced by the remains of a collapsed stone wall, now partly reclaimed by grass, with what appears to be an entrance gap on the southeastern side. The most fascinating feature, however, is found along the inner enclosure's northern wall: what seems to be the blocked entrance to a souterrain, one of those mysterious underground passages that dot the Irish landscape.

These souterrains, found throughout Ireland but particularly common in Ulster, were typically built between the early medieval period and the 12th century. They served various purposes; some were used for storage, others as hiding places during raids, and a few may have had ritual significance. The Gortnavern example, now sealed and silent, keeps its secrets well buried beneath centuries of accumulated earth and stone.