At Lackabane in County Cork, the record of an underground stone passage, a souterrain, rests entirely on a single second-hand account of a cavity that was opened and then closed again before anyone with a scholarly interest could get a look inside. A souterrain is a man-made underground structure, typically built from dry stone, used in early medieval Ireland for storage, refuge, or both. They are fairly common features in the Irish landscape, but they are usually at least visible. This one vanished back into the ground before it could be properly examined, and left no surface trace whatsoever.

The sole source is a reference from 1896, in which a writer named Quarry noted that a cavern had been uncovered in the area immediately beside a church at Lackabane. The circumstances of how it was opened are not recorded, nor is any description of what, if anything, was seen inside. It was closed before inspection could take place, and that is where the record ends. The associated church site survives as a separate monument, but the souterrain itself has never been re-examined or relocated. Whether it remains sealed beneath the ground, whether it has since collapsed, or whether the 1896 account was accurate in the first place, none of these questions have been resolved.