A shallow rectangular depression, measuring roughly 5.5 metres north to south and just a metre wide, drops no more than 20 centimetres below the surrounding surface. It is easy to overlook, but that modest dip in the earth may be all that remains visible of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically used for storage, refuge, or both, and now collapsed beneath the turf.

The depression projects inward from the enclosing scarp at the southern edge of the rath, a type of circular earthwork enclosure associated with early medieval settlement in Ireland, often interpreted as a defended farmstead. The relationship between souterrains and raths is well established across Ireland; the underground passages were frequently constructed within or beneath these enclosures, accessible from the interior. At Carbad More, the geometry of the feature, its rectangular form and its position pushing in from the boundary bank, is consistent with the profile of a roof that has gradually subsided as the supporting stonework beneath gave way over centuries. What was once a functional underground space has become little more than a faint scar in the landscape.