At around 270 metres above sea level, the summit of a steep-sided hill at Athgarrett in County Kildare carries a circular earthwork with no visible entrance. A bank of earth and stone, faced with stonework along its southern and north-eastern arc, defines a space roughly 58 metres across, and faint traces of a narrow outer fosse, a shallow defensive ditch, survive on the south-western side. Something was clearly meant to be enclosed here, yet the absence of any discernible gap in the bank makes it difficult to say how, or even whether, people regularly passed in and out.

The interior is now planted with trees, which gives the place a quietly formal appearance that sits oddly with the rugged hilltop setting. At its centre sits a low, roughly circular mound of earth and stone, about ten metres across at its base but narrowing to just two metres at the surface and rising only about sixty centimetres. This modest prominence is probably a trigonometrical station, one of the fixed survey points established across Ireland to support the Ordnance Survey's mapping work from the nineteenth century onwards. These stations were typically placed on high ground with clear sightlines, and the hilltop at Athgarrett would have served that purpose well. Whether the enclosing bank predates the survey work by centuries, or whether it has some connection to it, is not established. The earthwork itself, with its stone facing and possible fosse, has the character of something considerably older, though no date has been assigned to it.