This one in County Limerick came to light because a gas company was photographing its pipeline route from the air. On the 3rd of November 1984, aerial photographs taken for the Bórd Gáis Éireann Curraleigh gas pipeline captured what appeared to be a circular-shaped enclosure in a patch of pasture roughly 25 metres east of the R512 road at Ballygrennan. The feature had never appeared on any Ordnance Survey historic maps, and nothing on the ground would tell you it was there at all.

The enclosure belongs to a class of monument sometimes described simply as a ringwork or earthwork enclosure, a broad category that can encompass everything from early medieval farmsteads to prehistoric ceremonial sites. What makes this particular example so elusive is that by the time aerial survey technology caught up with the landscape in the form of OSi orthophotos taken between 2005 and 2012, and again on a Google Earth image dated 20th September 2020, no surface remains were visible whatsoever. The ground had, to all appearances, swallowed the feature entirely. A field boundary running roughly east to west cuts across the area, and a dwelling house sits to the southeast, both of which have further complicated or truncated whatever traces once existed. A second enclosure, recorded separately in the Sites and Monuments Record as LI040-003, lies immediately to the north, hinting that this corner of Limerick may once have seen more sustained activity than the current pastoral quiet suggests. The record was compiled by Martin Fitzpatrick and uploaded in May 2021.

For anyone curious enough to visit, the site sits in private farmland close to the R512, and there is genuinely nothing to see at ground level. The value here is less in the visit itself than in what the story illustrates: that the Irish landscape holds features detectable only from altitude, or in certain light conditions when low sun picks out faint cropmarks or soil discolouration. If you do pass along the R512, the flat pasture to the east gives little away, which is rather the point.