There is no visible surface trace of it. You could walk directly over it and have no idea it was there.

A souterrain is an underground passage or chamber, typically dry-stone built, associated with early medieval settlement in Ireland. They were used variously for cold storage, refuge, or concealment, and they survive in considerable numbers across the country, though many remain unlocated or poorly documented. The example at Barrahaurin was recorded by Hartnett in 1939, who noted the cramped entrance, the inward-leaning stone walls, and a roof formed by four transverse lintels laid across the top. The floor, when he examined it, was littered with debris, and the interior was obscured enough that he could not determine whether a second chamber lay beyond the first. That question appears to remain unanswered.