It is the kind of thing you could stand on without realising it, a slight swelling in the earth measuring roughly six metres north to south and five metres east to west, lifting only about a third of a metre above the surrounding surface at its highest point. Yet that modest bump conceals a dry-stone passage, built without mortar, its roof formed from flat capstones laid horizontally as lintels across the walls.

The souterrain, which is an underground stone-built passage or chamber typically associated with early medieval settlement in Ireland, sits within the western half of a rath, a type of enclosed farmstead usually defined by one or more earthen banks and ditches, and common across the Irish landscape from roughly the sixth to the twelfth centuries. Souterrains were often incorporated into such enclosures, likely serving as storage spaces for perishables or as places of refuge. At Breaghwy, the passage is narrow, around 0.8 metres wide, and the infill of soil has rendered it completely inaccessible. Two lintelled openings remain visible at the northern and southern ends of the raised area, hinting at the structure beneath without yielding any further access.

What survives here is fragmentary in one sense, yet strangely coherent. The rath that contains it is a recorded monument in its own right, and the souterrain's two open throats, still framed by their original stonework, suggest a construction that has held its shape underground even as the passage itself has quietly filled over the centuries.