The opening, just a metre high and barely sixty centimetres wide, has been frustrating curiosity for at least two centuries. It marks the entrance to a souterrain, an underground passage or chamber typically built during the early medieval period, often for storage or refuge, cut into the earth beneath or beside a cashel, the Irish term for a stone-walled ringfort. What makes this one quietly compelling is how consistently it has defeated investigation while remaining visible and mapped.

The place was already known by the time the Ordnance Survey recorded it as a "cave" on their six-inch maps of 1840, and the label persisted on the 1916 edition. John O'Donovan, the scholar and place-name researcher who worked extensively with the Ordnance Survey, visited in 1830 and noted that the passage was open at that point, though he considered it inaccessible on account of the narrowness of the passage. By 1900, when the antiquarian Thomas Johnson Westropp documented it, the situation had changed further; he described it simply as closed. Whether that closure was deliberate or the result of gradual collapse or silting, he did not record. The entrance now sits roughly eight metres from the centre of the cashel, within the south-eastern quadrant of its enclosing wall, sealed with timbers that give no indication of their age.