The structure is a souterrain, an underground gallery built without mortar from carefully stacked drystone, and it takes the form of an L-shape stretching more than fourteen metres in total length. What makes it particularly absorbing is not its size but its internal logic: two separate passages joined by a creep, a deliberately narrow connecting shaft that would have forced anyone moving through it to drop down and squeeze forward. That kind of bottleneck was almost certainly intentional, designed to slow an intruder or conceal a second chamber from anyone who did not know it was there.

The first passage runs roughly southeast to northwest and measures nine metres long, though at just thirty centimetres high it has been rendered entirely inaccessible by partial collapse, as has the creep itself, which narrows to only half a metre wide. Near the northwest end of the creep's southern wall, traces of a small recess running north to south have been noted; this may represent an air vent or the beginning of a third passage altogether. The second passage, running northeast to southwest for around five metres, survives in better condition, standing between 1.2 and 1.5 metres high and wide enough to move through upright. Entry into this section is possible via a breach at its northeastern end. Souterrains of this kind were constructed throughout early medieval Ireland, typically in association with cashels, the stone-walled enclosures that served as defended farmsteads. They are generally dated to the early Christian period, roughly the sixth to twelfth centuries, and were likely used for food storage, refuge, or both.

The second passage remains accessible through the breach at its northeast end, though the collapsed state of the first passage and the creep means the full extent of the souterrain cannot be followed through. The traces of the possible recess near the creep's side wall are worth looking for if the ground conditions allow, as they hint at a more complex arrangement than the surviving plan immediately suggests.