It does not appear on the Ordnance Survey's historic maps, has no marker, no signage, and no formal name beyond the townland it happens to occupy. For most of its existence it has been exactly what it looks like from ground level: a patch of pasture. Only from the air does the geometry become legible, a near-perfect ring roughly 21 metres across pressed faintly into the soil, the kind of shape that takes centuries of settlement and abandonment to produce.

The enclosure at Ballygrennan was identified through aerial photography, specifically an Archaeological Survey of Ireland photograph taken on 4 March 2006, which caught the site under conditions that made the cropmark visible. Cropmarks of this kind appear when buried or levelled earthworks affect how vegetation grows above them; differences in soil depth and moisture cause grass or crops to ripen unevenly, tracing the outline of structures that are otherwise invisible at ground level. The circular form, approximately 21 metres in diameter, is consistent with a ringfort or similar enclosed settlement, the sort of site that was once commonplace across the Irish countryside and typically dates from the early medieval period, though without excavation the precise date here remains unknown. What complicates the picture is a field boundary running east to west across the northern edge of the enclosure. That boundary is post-1700 in origin, meaning it was laid down after the monument was already levelled, cutting through whatever remained and leaving the circular cropmark intersected at the north. The site sits roughly 260 metres north of the townland boundary with Ballyguileataggle, and its absence from historic mapping suggests it had already been reduced to nothing visible before surveyors came through. The record was compiled by Fiona Rooney and uploaded to the Archaeological Survey of Ireland database in April 2021.

The enclosure is not accessible as a visitor site and there is nothing to see on the ground in any conventional sense. The field remains in agricultural use. The most legible version of this place exists in the 2006 aerial photograph and in a Google Earth orthoimage dated 28 June 2018, both of which show the cropmark clearly enough to trace the arc of the original boundary. For anyone interested in the archaeology of the Irish midlands and west, the Survey of Ireland's database offers the coordinates and imagery; the site itself asks for a tolerance of invisibility that most archaeological monuments, however modest, do not require quite so completely.