Catalogued simply as Site J, it survives today as roughly three-quarters of whatever it once was, its northern portion either removed at some point in the centuries since it was built, or possibly never constructed in the first place. That ambiguity is built into its very shape: crescentic, curving like a partial arc, measuring approximately 4.75 metres east to west and 3.5 metres north to south, and standing no more than 20 centimetres at its highest point. A cairn, in its simplest definition, is a mound of stones raised by human hands, often as a burial or memorial marker. This one leaves the precise intention open.

Site J forms part of a much larger complex on and around Piperstown Hill, described by researchers Rynne and Ó hEailidhe in 1965 as an extensive settlement and cemetery dating to the Late Neolithic and Early Bronze Age, a period spanning roughly from around 3000 BCE into the second millennium BCE. That a site of this age and apparent scale exists in the Dublin Mountains is not widely appreciated. The cairn has no surviving kerb, which is the ring of upright stones that typically edges and defines such monuments, making it harder to read and easier to overlook. What remains is low, undemonstrative, and easily mistaken for a natural scatter of stones.

Piperstown Hill sits within the Glenasmole area of the Dublin Mountains, accessible from the south of the city. The southern slopes where Site J lies can be reached on foot, though the terrain is open hillside rather than maintained path. The cairn's low profile means that knowing roughly where to look matters considerably; arriving with the site's grid reference or a detailed map makes a real difference. Given the modest height of the surviving structure, low-angle winter light, which rakes across the ground and picks out subtle rises, can help reveal the crescent outline far better than a visit in flat summer brightness.