Somewhere beneath a field of reclaimed pasture in County Limerick, the outline of a rectangular earthwork survives only as a cropmark, a ghostly impression that shows up in aerial photographs but leaves no trace whatsoever on the ground. No bank, no ditch, no ridge interrupts the grass. The structure exists, in any practical sense, only as a pattern in cereal crops photographed from altitude.

Cropmarks form when buried features such as ditches, walls, or pits affect how plants grow above them. Ditches retain moisture and produce taller, greener crops; buried stone foundations drain quickly and stunt growth. From the air, these differences in crop height and colour resolve into shapes that are otherwise entirely invisible. The earthwork at Coolalough was identified in exactly this way during the Bruff aerial photographic survey of 1986, recorded under reference AP 5/2077. The survey image shows a rectangular cropmark intersected at its southern edge by a field boundary running roughly east to west, placing the feature approximately 200 metres east of the townland boundary with Kilfrush, and 110 metres to the south-west of a neighbouring site. Whether the underlying feature is an enclosure, a building platform, or something else entirely remains uncertain; the record classifies it only as a possible earthwork. By the time Digital Globe and Google Earth orthoimages were reviewed, sometime between 2011 and 2013, no surface trace remained.

For anyone curious enough to visit, the site sits in ordinary agricultural land with no visible indicator of anything beneath it. The cropmark, if it reappears at all, would only be legible from the air and only during the right growing conditions, typically a dry spell in early summer when moisture stress makes buried features most legible to a camera. The 1986 survey image, compiled by Fiona Rooney and uploaded to the record in June 2021, remains the clearest evidence that anything is there at all.