A field on a west-facing slope in Killeenduff, County Sligo, is recorded as the site of a souterrain, one of the stone-lined underground passages and chambers that were built throughout early medieval Ireland, used variously for storage, refuge, and purposes that remain debated by archaeologists. The unusual thing about this particular site is that, by the time anyone went to look at it properly, there was nothing left to see.

The site never appeared on any edition of the Ordnance Survey six-inch maps, the detailed series that from the nineteenth century onwards captured field boundaries, raths, standing stones, and the subtler imprints of earlier habitation across the Irish landscape. It was also absent from the Sites and Monuments Record compiled in 1989, which attempted to catalogue the known archaeological heritage of the country. It did eventually make it into the Record of Monuments and Places in 1995, suggesting that some evidence or local knowledge had brought it to official attention in the intervening years. When an inspection took place in 2003, however, the pasture showed no visible remains at ground level whatsoever. No earthwork, no hollow, no exposed stonework; nothing to indicate that anything lay beneath or had ever been there at all.