A souterrain is an underground stone-lined passage or chamber, built during the early medieval period, typically associated with ringforts and used variously for storage, refuge, or concealment. At Cloonteens, both the souterrain and the ringfort it belonged to have effectively vanished from the surface of the landscape, one levelled by time and land use, the other buried beneath it.

The only firm historical record of the souterrain comes from Bowman, writing in 1934, who noted its presence within the fort. The ringfort itself, a circular enclosure of the kind that once numbered in the tens of thousands across Ireland, has since been levelled, leaving no visible trace above ground. Without that enclosing bank and ditch, there is nothing on the surface to mark where the settlement once stood, let alone where its underground chamber lies. The souterrain survives, if it survives at all, as an absence, known only through a single bibliographic citation and the reasonable assumption that what was recorded in 1934 has not simply ceased to exist.