Souterrains are underground passages or chambers, typically stone-lined, built during the early medieval period and associated with ringforts across Ireland. Their precise function is still debated, though storage, refuge, and ventilation of nearby structures have all been proposed. What makes this particular feature quietly arresting is its geometry: visible from the surface as a sunken outline, it reads almost like a diagram of itself, the earth having settled into the shape of the tunnel system beneath.

The structure was noted by Neary in 1914, who described it as a dug-out souterrain, suggesting it was cut directly into the subsoil rather than constructed from built stone. The main axis runs roughly north-west to south-east and stretches twelve metres in length, with a shorter arm of four metres branching off to the south-west at roughly the midpoint, producing the T-plan that remains legible at ground level today. Its central position within the associated ringfort, a roughly circular enclosure defined by an earthen bank and ditch, is typical of the relationship between these two monument types, where the souterrain would have served whoever occupied the enclosed settlement above.