This is a souterrain, an underground passage built from dry-laid stone without mortar, roofed with flat lintel slabs, and narrow enough that anyone entering would have to crawl. The passage is roughly 85 centimetres wide and only 42 centimetres high, dimensions that speak to a deliberate, functional design rather than any grand architectural ambition.

Souterrains are a recurring feature of early medieval Ireland, typically associated with raths, the circular earthwork enclosures that served as farmsteads from roughly the sixth to the twelfth century. This one sits slightly west of centre within just such a rath, the earthen bank of which still defines the site today. The passage appears to run for approximately eight metres in a west-south-westerly direction, heading towards that enclosing bank. The evidence for its full extent is indirect: patches of grassed-over surface collapse trace its probable course, the ground having settled where the roofing has weakened over centuries underground. Whether souterrains were used for food storage, refuge, or both is still debated, but their placement within a rath's interior is entirely typical, and the drystone construction here is consistent with the wider tradition found across Ireland.