Not demolished, not filled in, simply gone from sight, leaving no trace that anything was ever there.

The feature in question is a souterrain, an underground stone-lined passage or chamber typically constructed during the early medieval period, often associated with raths, the circular earthen enclosures that served as enclosed farmsteads across Ireland. This particular souterrain sits within one such rath, and on both the 1838 and 1919 editions of the Ordnance Survey six-inch maps it is marked in the north-west quadrant of the enclosure under the label "Cave", which was a common enough term used by early surveyors for underground structures they could observe but not fully explain. That it appears on both maps, separated by more than eighty years, suggests it was recognisable at ground level well into the early twentieth century. At some point after 1919, whatever opening or depression once indicated its presence was lost, smoothed over, or simply collapsed inward without drama or record.