A shallow depression roughly a metre across, packed with square limestone blocks, marks what was once the entrance to an underground passage. A broken roof lintel protrudes on the north-north-west side, and a fragment of drystone walling is visible to the south-south-east. Beyond that, the structure curves away to the south-west, beneath the turf, largely unexcavated and unexamined.

What lies beneath is a souterrain, a type of man-made underground passage or chamber built in Ireland predominantly during the early medieval period, roughly between the sixth and twelfth centuries. Souterrains were typically constructed from drystone walling, roofed with large flat lintels, and then covered over with earth. Their precise function has long been debated; storage of perishables, refuge during raids, and simple concealment have all been proposed, and different sites may have served different purposes. The Carraghy example follows the familiar construction method: local limestone shaped into walls and capped with flat stones, before the whole thing was buried. The curve in its plan, visible even from the surface collapse, is a feature found in other souterrains across the west of Ireland, possibly designed to slow unwanted entry or to regulate airflow.