A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, and used variously for storage, refuge, or both. The one at Kippagh has left nothing visible at the surface, its existence betrayed only by a slight hollow in the ground.

The evidence for it comes from a single observation recorded by Bowman in 1934. Writing about the ringfort in which it sits, he noted a depression on the southwest of the interior, and concluded that it indicated the site of a souterrain below. A ringfort, to give context, is a roughly circular enclosure defined by an earthen bank and ditch, the most common type of early medieval farmstead in Ireland. The souterrain would have been constructed as an adjunct to whatever settlement once occupied that enclosure. Whether it survives intact underground, collapsed, or partially filled is unknown.