On the east-facing slope of a broad hill in County Waterford, the first edition Ordnance Survey six-inch map of 1840 marks something intriguing inside the outline of an ancient rath: a cave. A rath is a circular earthen enclosure, typically dating from the early medieval period and used as a farmstead or place of habitation, and caves found within or near them occasionally turn out to be souterrains, stone-lined underground passages that served as storage spaces or places of refuge. The label on that early map, drawn when local memory of the landscape was still being systematically gathered for the first time, suggests that something was known to exist there, or was at least believed to.

The difficulty is that no physical trace of any such feature survives above ground today, and no local knowledge of it appears to have been preserved either. Whatever the cartographers recorded in 1840, whether a genuine underground passage, a natural hollow, or simply a rumour given ink and paper, it has since vanished from both the earth and living memory. This kind of quiet disappearance is not unusual in Irish archaeology. Souterrains were sometimes deliberately backfilled, collapsed gradually over centuries, or simply forgotten as farming practices changed and the raths they sat within were absorbed into field systems. What is slightly unusual here is the gap between the confident marking on the map and the complete absence of any subsequent evidence.