That label points to a souterrain, an underground stone-lined passage or chamber typically built during the early medieval period to serve as a storage space or place of refuge, and its presence here is one of the more quietly telling details about this site at Ballinbranhig.

The rath itself is a univallate ringfort, meaning it has a single enclosing bank rather than the multiple concentric rings found at higher-status sites. It measures 41 metres in internal diameter and presents today as a sub-rectangular area with curved corners, enclosed by a low bank of earth and stone. The bank stands 1.3 metres high on the outside but only 0.45 metres above the interior floor, which sits at a slightly lower level than the surrounding land. That asymmetry is worth noting: it suggests the interior was deliberately scooped down, or that the bank material was piled outward for effect. A bohareen, a narrow rural lane, has cut across the northern to north-eastern arc of the enclosure, removing part of the original circuit. The probable entrance on the western side is 2.5 metres wide. Elsewhere in the western sector, three low mounds survive, measuring roughly 4 to 6 metres in length and 3 metres in width, which are all that now visibly remains above ground in the interior. These could represent collapsed structures, though nothing more specific can be said with certainty. The site was documented in the North Kerry Archaeological Survey compiled by C. Toal and published in 1995.

The souterrain recorded by the nineteenth-century surveyors as a 'cave' is catalogued separately but falls within the same enclosure. Visitors approaching the area should be aware that the bohareen bisects the northern edge, so the circuit as it originally stood no longer reads as complete from ground level. The three interior mounds in the western sector are low and unobtrusive, easily overlooked without prior knowledge of what to expect.