A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, often used for storage, refuge, or both. This one sits on top of the knoll rather than tucked into a hillside, which is a less common situation and raises quiet questions about how it was originally approached and what purpose it served the community that built it.

Local information recorded in the early twentieth century suggests the passage was still accessible in the 1920s, meaning people living in the area could still locate and enter it within living memory of that time. Since then it has closed, whether through deliberate infilling, gradual collapse of the roof stones, or simply the slow accumulation of soil and vegetation over a forgotten entrance. The knoll itself remains, a slight but distinct rise in otherwise level farmland, the kind of landscape feature that tends to accumulate archaeological interest precisely because generations of farmers found it easier to plough around than through.