A ploughshare turned it up at some point, breaking into a void beneath the soil, and local memory kept the knowledge alive. No masonry protrudes above ground, no hollow in the turf marks its course, and nothing visible signals its presence to anyone walking across the field today.

The structure is a souterrain, a type of underground passage or chamber built during the early medieval period in Ireland, typically by corbelling or lining stone to create a dry, concealed space that may have served for storage, refuge, or both. What makes the Ballyfilibeen example quietly curious is its proximity to a moated site lying roughly 250 metres to the south-south-east. Moated sites, enclosures surrounded by a water-filled or dry ditch, are generally associated with Anglo-Norman rural settlement from the thirteenth and fourteenth centuries, making them considerably later in origin than the souterrain tradition. Whether the two features were ever connected in function or simply occupy the same stretch of farmland by coincidence is unknown, but the clustering of different periods of occupation in a single landscape is not unusual in this part of Mid Cork.