A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts and used variously for storage, refuge, or both. This particular one, located in the south-western quadrant of the ringfort at Kilpatrick, had already left the visible world by the mid-twentieth century. By 1940, the Ordnance Survey was marking it not as an existing feature but as a "site of", meaning cartographers at the time recorded only the memory of it, or the inference of it, on the landscape.

The ringfort itself, a circular enclosed settlement of the type that dots the Irish countryside in its thousands and dates broadly to the early medieval period, contains a second point of interest. A further possible souterrain has been identified in the northern half of the same enclosure. That it is described as "possible" speaks to the uncertainty that attaches to underground features once the surface evidence has gone. Whether through agricultural activity, collapse, or the slow work of soil movement over centuries, both features have become effectively invisible at ground level, known now only through earlier mapping and archaeological inference.