This one in Tankardstown, County Limerick, does none of that. It exists, in any meaningful sense, only in a single aerial photograph taken on the 3rd of November 1984, visible as a faint circular cropmark pressed into wet pasture. On the ground, there is nothing to see. On satellite imagery, nothing either. The site was never marked on the Ordnance Survey's historic maps, and orthophotos taken between 2005 and 2012 confirmed what most visitors would discover for themselves: the field looks like a field.

The photograph in question was taken during an aerial survey commissioned by Bórd Gáis Éireann for the Curraleigh West to Limerick gas pipeline. Archaeologists routinely examine such surveys for anomalies, and it was during this examination that a possible ditch barrow was identified, logged as site number 040242. A ditch barrow is a prehistoric burial monument defined by a circular or near-circular ditch, sometimes with an internal mound, built to mark or contain the remains of the dead. The cropmark here, faint but circular, suggested the buried outline of just such a feature. It sits to the west of a broader cluster of barrows and an enclosure recorded nearby, which lends the identification a degree of plausibility, since prehistoric monuments of this kind tend to appear in groups rather than in isolation. The record was compiled by Fiona Rooney and uploaded to the national monuments database in May 2021.

There is, practically speaking, nothing to visit in the conventional sense. The site lies in rough wet pasture and leaves no impression on the surface whatsoever. Its interest is of a different kind, the idea that a buried circular ditch, dug perhaps three or four thousand years ago, remained entirely invisible until an aircraft happened to pass overhead on a November afternoon during a survey for a gas pipeline. Anyone curious enough to locate the general area near Tankardstown will find themselves looking at ordinary farmland, which is in its own way the point. The archaeology here is entirely subsurface, detectable only under specific conditions of soil moisture and crop stress, and documented now in little more than one archived photograph and a database entry.