What looks at first like an uneven dip in the grass is actually the collapsed outline of an underground passage, a souterrain, its shape still legible as a broad T pressed into the earth. Souterrains are stone-lined tunnels built during the early medieval period, most commonly associated with ringforts, and used for storage, refuge, or both. This one has not been excavated, so its roof and walls are gone, but the hollow they left behind remains, and its geometry is precise enough to make clear what once lay beneath.

The longer arm of the T runs east to west, stretching 10.8 metres in length, averaging around 2.8 metres in width, and dropping to as much as 1.3 metres in depth at its eastern end. Roughly halfway along, a second passage branches off to the south, measuring 2.8 metres long and nearly as wide. Together they form the characteristic branched plan that appears in souterrains across Ireland, where a main corridor connects to one or more side chambers. This particular souterrain sits in the north-eastern quadrant of a ringfort, the circular earthwork enclosure that would originally have enclosed a farmstead or small settlement. The pairing of ringfort and souterrain is common, but the survival of the surface outline here, clear enough to measure and map, gives this site an unusual legibility for something so long underground.