A souterrain is an underground stone-lined passage or chamber, typically constructed during the early medieval period in Ireland as a place of refuge, cold storage, or concealment. This one has left no trace on the surface, and the only evidence that it exists at all is a shallow depression observed in 1974 by the Office of Public Works, a slight dip in the ground that suggested something hollow underneath.

What gives the site an extra layer of interest is its proximity to a now-levelled moated site roughly 140 metres to the south-south-east. Moated sites are enclosures surrounded by a water-filled or wet ditch, most commonly associated with Anglo-Norman settlement in Ireland during the thirteenth and fourteenth centuries. The moated site at Garrane is itself gone, flattened by centuries of agriculture, which means that two distinct archaeological features in the same small area have effectively vanished from view. Whether the souterrain predates the moated site or was in some way connected to the settlement that produced it is not recorded, but the pairing is suggestive of a landscape that was once considerably more active than its current silence implies.