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 ventilation. This one was found, covered over again, and left to sit in silence beneath the earth, its location known mainly through local memory rather than any visible marker.

The souterrain lies within a rath, a circular earthwork enclosure of the early medieval period, usually the remains of a farmstead defended by one or more banks and ditches. At Leaffony, local information records that the souterrain was discovered beneath a large flat stone in the interior of the rath. Once uncovered, it was sealed again, and the ground above it was left undisturbed. There is now no visible trace at surface level. The discovery passed without excavation or detailed recording, and what lies beneath, its extent, its condition, whether it retains any of the structural features typical of such passages, remains unknown.