Inside that gap, beneath tall grass, sits a low earthwork that most people would walk over without registering it at all. The site at Ballygrennan is not dramatic by any measure, but its quiet separation from the encroaching conifers gives it an oddly purposeful quality, a small circle of older ground that has been, however modestly, acknowledged.

This is a rath, the Irish term for a ringfort, which was the standard form of enclosed rural settlement in early medieval Ireland, typically dating from roughly the fifth to the twelfth centuries. Thousands survive across the country, though many are far more imposing than the one at Ballygrennan. This example sits on low-lying, marshy ground, and its defining feature is a scarped edge, essentially a cut or trimmed bank where the interior ground level drops away, running roughly circular at approximately 18.2 metres north to south and 16.6 metres east to west. The bank itself stands only about 0.6 metres high and 1.2 metres wide. That is modest even by ringfort standards, and the interior, as recorded by Denis Power when the site was compiled for the record in 2011, appears level and entirely featureless beneath the meadow cover. An aerial photograph taken in October 2002 for the Archaeological Survey of Ireland provides the clearest picture of the site's form from above.

The rectangular fenced enclosure around the earthwork means the site is at least marked out and protected from tree planting, which is something. Locating it requires attention, since the meadow grass is tall and the scarped edge is subtle enough that the eye needs a moment to read the slight change in ground level. The marshy surroundings are worth bearing in mind underfoot, particularly in wetter months. There are no facilities, no signage, and no formal access point; this is agricultural land with a fence around an old earthwork in the middle of it, and the experience of finding it is more or less exactly that.