What the low earthwork marks, however, is the roof line of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, typically used for cold storage, refuge, or both. The surface expression here is modest: a north-to-south axis of about seven and a half metres, crossed by an east-to-west arm of roughly the same length, the whole thing reading as a slight undulation in the grass rather than anything that announces itself.

The souterrain sits to the north of the centre of the ringfort it belongs to, recorded as MA118-051. Ringforts, the circular enclosed farmsteads that dot the Irish countryside in their thousands, frequently contained souterrains as functional annexes to domestic life, and this pairing follows that well-established pattern. The site falls within the Ballinrobe district, in a landscape bounded by Lough Mask to the west and Lough Carra to the east, a stretch of south Mayo that was surveyed archaeologically in the early 1990s. At the time that survey was carried out, the souterrain itself was inaccessible, meaning the underground structure had not been entered or formally examined, and its internal layout, construction method, and condition remained unrecorded beyond what the surface geometry could suggest.