It is a souterrain, a type of underground stone-lined tunnel constructed in early medieval Ireland, typically associated with ringforts and used variously for storage, refuge, or both. This one is built in drystone, meaning its walls were laid without mortar, and its two axes meet at an angle: a longer east-west run of roughly fourteen metres, and a shorter north-south branch extending about six metres from the southwest end.

What makes the structure visible at all is, paradoxically, its partial ruin. Several of the large flat roof lintels spanning the main passage have collapsed inward, opening gaps along the length of the tunnel that allow a person to peer down into the stonework below. The rest remains buried and probed only indirectly, its full extent mapped by pushing rods into the ground above rather than by any direct entry. The rath it sits within, a roughly circular earthwork enclosure of the kind widespread across early medieval Ireland, has its own separate record, and the souterrain occupies just one quadrant of that larger site. The combination of enclosure and underground chamber is a common enough pairing in the Irish archaeological record, though that familiarity does little to diminish the oddness of standing above a hidden stone corridor and knowing it threads away beneath your feet in two directions at once.