This one barely exists at all. A roughly rectangular enclosure in pastureland near the Ballygrennan townland boundary in County Limerick has no surface trace visible to a visitor on the ground, no entry on the Ordnance Survey's historic maps, and no certain explanation. What it does have is a fleeting presence in aerial photography, appearing and disappearing across a span of decades like something the land occasionally decides to show.

The site first came to light on 3 November 1984, when aerial photographs were taken as part of the Bórd Gáis Éireann gas pipeline survey, a project that, by necessity, swept cameras across large stretches of Irish countryside and incidentally recorded a good deal of previously undocumented archaeology. Examination of those photographs identified what appeared to be a square-shaped enclosure. Later orthoimage data from Digital Globe, captured between 2011 and 2013, showed it more clearly as a rectangular area measuring approximately 21 metres north to south and 23 metres east to west, defined on its southern, western, and northern sides by a linear depression, with a field boundary cutting across its eastern edge. An enclosure of this general type, a defined area set apart from the surrounding landscape by a bank, ditch, or other boundary, could serve any number of purposes across Irish history, from settlement to agriculture to ritual. But the record compiled by Martin Fitzpatrick offers a cautionary note: the linear features may simply represent drainage channels associated with reclamation and landscaping works connected to nearby Greenpark House, situated roughly 850 metres to the southwest. By a Google Earth image dated September 2019, no surface remains were visible at all.

There is nothing for a visitor to see here in any conventional sense. The site sits in working pasture, within a field system, and the ground gives nothing away. Its interest lies entirely in what aerial observation revealed and then, in a sense, took back. For anyone tracing the gas pipeline corridor through Limerick, or studying how landscape interventions around eighteenth and nineteenth century estate houses reshaped and obscured earlier features, this small, ambiguous rectangle repays attention, not as a place to visit, but as a reminder of how much archaeology exists only in archive photographs rather than in the earth itself.