On top of Kilmacomb Hill in County Waterford, the Ordnance Survey maps of 1840 and 1925 both mark a circular enclosure of roughly 55 metres in diameter, labelling it, with a certain folkloric confidence, a fairy ring. The label has persisted across nearly a century of cartography, yet if you were to climb the hill today, you would find nothing at ground level. No stones, no ring, no visible trace of whatever the surveyors thought they were recording.

The puzzle deepens when you look at what earlier writers believed they saw. Richard Ryland, writing in 1824, and Samuel Lewis, in his 1837 topographical dictionary of Ireland, both describe five large stones set within a stone circle of around 30 metres in diameter on Kilmacomb Hill. That is a fairly specific claim, and two independent observers making it within thirteen years of each other lends it some weight. The working theory now, however, is that neither man may have been describing what they thought they were describing. About a kilometre to the north-east, near Harristown, there is a genuine passage tomb, a prehistoric monument of the type in which a stone-lined corridor leads to a burial chamber beneath a mound. It is possible that Ryland and Lewis were actually recording that structure, and that the Kilmacomb Hill attribution was a matter of confusion about location rather than invention of detail. Somewhere between two nineteenth-century writers, two editions of the OS six-inch map, and a hilltop rock outcrop, a monument has either vanished or never quite been where anyone said it was.