It was a practical label for something older and more deliberate: a souterrain, an underground stone-lined passage or chamber typically built during the early medieval period, often beneath or beside a rath, and used variously for storage, refuge, or both.

The site at Ballinbranhig sits within a univallate rath, a single-banked enclosure of the kind that once served as a farmstead for an early Irish family. The rath itself survives as a sub-rectangular area with curved corners, enclosed by a low earth and stone bank, its interior lying at a slightly lower level than the surrounding land. A bohareen, a narrow rural laneway, cuts across the northern to north-eastern side of the enclosure, interrupting what would once have been a continuous boundary. The souterrain beneath the interior is no longer accessible or visible as a passage. What remains above ground, towards the western sector, are three grassy mounds measuring roughly four to six metres in length, the collapsed or filled remnants of what the older map recorded. The possible entrance to the souterrain is thought to lie on the western side, where a gap of about 2.5 metres is still apparent. C. Toal documented the site in the North Kerry Archaeological Survey, published in 1995, and it is from that record that the surviving measurements and observations derive.