It is easy to walk past without registering what it is. The circular enclosure measures just 12.6 metres across internally, its defining bank ranging between one and two metres wide and standing no more than 0.8 metres high at its tallest. Whatever entrance it once had, and whatever fosse, a ditch dug around the outside of such a structure, may have accompanied it, both have been lost to disturbance. What remains is a subtle earthwork, the kind that rewards patient attention.

This site is the most southerly of three enclosures on this part of Three Rock Mountain, the other two recorded under the monument numbers DU025-028001 and DU025-028002. All three were already significant enough to be marked on the Ordnance Survey six-inch map of 1843, one of the earliest systematic surveys of the Irish landscape, which means they were visible and recognisable features to nineteenth-century surveyors. Enclosures of this general type, roughly circular areas defined by a bank, occur across Ireland in a wide range of periods and contexts, from early medieval settlement enclosures to prehistoric ritual sites, and without excavation it is difficult to assign a firm date or function to any individual example. The site was compiled by archaeologists Geraldine Stout and Padraig Clancy, with a revised record uploaded in July 2018.

Three Rock Mountain is accessible from several points on the southern fringes of Dublin, and the forestry plantation that now covers this part of the summit means the enclosure sits in an environment quite different from the open hillside the 1843 surveyors would have known. The tree cover changes the light and the sense of scale, and the earthwork can read as little more than an uneven rise in the ground until you stand close enough to trace its circuit. It is worth walking the full circumference slowly, since the bank height varies and the overall shape becomes clearer from certain angles. Going in autumn or winter, when the understorey is thinner, makes the earthwork easier to read.