That qualifier, unusually candid for an archaeological record, is essentially the whole story. A souterrain is an underground stone-lined passage or chamber, typically built during the early medieval period in Ireland and associated with nearby settlement sites, used variously for storage, refuge, or both. The one at Cloonee is remarkable chiefly for existing, in the official record at least, as little more than a pencil mark on a nineteenth-century map.

The sole evidence for the site is a symbol on a second-edition Ordnance Survey six-inch map extract, a series produced in Ireland from the 1890s onwards. No source for that mark was ever recorded, no fieldwork accompanied it, and no local knowledge has since confirmed that anything lies beneath the ground at the indicated spot. Because the uncertainty around its nature and origin is so complete, the site was formally excluded from the archaeological inventory rather than included with a caveat. It is, in the language of the discipline, a possible souterrain, which is a careful way of saying that someone, at some point, thought something was there.