On the south-south-western side of a historic enclosure in Cloonagleavragh, County Sligo, the remains of a souterrain survive in a state that is more suggestive than legible. 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 concealment. Here, the passage is blocked and inaccessible, leaving only two surface features to mark its presence.

The first is a roughly rectangular spread of small rubble stone, running approximately six metres on its north-east to south-west axis and about one and a half metres wide, which appears to represent a filled-in or collapsed entrance. Immediately to its north-east lies a circular, bowl-shaped depression roughly two metres across and about twenty centimetres deep. That shallow dip in the earth is thought to indicate a section of the souterrain passage that has given way beneath the soil, the ground quietly subsiding over what was once a roofed underground void. The souterrain sits within a wider enclosure recorded separately, suggesting this was once a settled and organised agricultural or domestic site, the underground feature serving the community that lived within those enclosing banks or walls.