At Kilphillibeen in County Cork, a souterrain, an underground stone-lined passage or chamber typically associated with early medieval settlement, once ran beneath the ground inside a ringfort. It has since been filled in, leaving no visible surface trace whatsoever.

Souterrains were a common feature of Irish ringforts, the circular enclosed farmsteads that dot the Irish countryside in their thousands and date mainly to the early medieval period, roughly 500 to 1000 AD. Their precise function is still debated, though they are generally thought to have served as storage spaces for perishables, refuges in times of danger, or both. The one at Kilphillibeen sat within a ringfort that still exists as a recorded monument, but the souterrain itself is gone, its void collapsed or deliberately packed with fill at some point before the site was formally noted. No date is given for when this happened, and no description survives of what the passage looked like or how extensive it was.

What remains is essentially an absence. The ringfort itself may still hold some trace in the landscape, but the souterrain has left nothing a visitor could identify or stand over. It exists now only as a category, a label applied to something that can no longer be seen or entered.