A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, and thought to have served for storage, refuge, or both. This one has been closed up, its entrance sealed, and the ground above it gives nothing away. No hollow in the turf, no slight depression, no scatter of displaced stone. It is, for all practical purposes, invisible.

The only record of its existence comes from Bowman, writing in 1934, who placed it at roughly twenty yards west of a nearby fort, the kind of ringfort with which souterrains are frequently associated across the Irish landscape. That proximity is archaeologically significant; the pairing of a defended enclosure with an underground passage was a common arrangement in early medieval Ireland, suggesting the two features likely belonged to the same period of occupation. Beyond Bowman's brief note, the details are sparse. The souterrain at Curraghs is less a site than a reference, a single sentence in a mid-twentieth century account pointing at a piece of ground that has since closed over it entirely.