Souterrains are underground passages or chambers, typically stone-lined, built during the early medieval period and associated with ringforts across Ireland. They served various purposes, most likely food storage, refuge, or both. At Ardnageehy, the evidence on the surface is minimal: a slight hollow measuring roughly two metres east to west and one metre north to south, suggesting that the chamber beneath has given way and the roof has collapsed inward.

The ringfort it belongs to is a separate recorded monument in its own right, and the souterrain sits within the southern portion of that enclosure. Ringforts, which are circular areas defined by earthen banks or stone walls, were the most common form of rural settlement in early medieval Ireland, and it was common practice to construct souterrains within them. The depression at Ardnageehy is quiet, unassuming evidence of that tradition, though whether the chamber is wholly collapsed or partly intact underground remains uncertain from surface observation alone.

The site is modest by any measure, and a visitor arriving without prior knowledge might walk past the depression without registering its significance. What makes it worth pausing over is precisely that modesty: a slight dip in a field, within the footprint of a long-disused enclosure, quietly indicating that something once lay beneath.