A cairn is simply a mound of heaped stones, usually covering a burial or marking a significant point in the landscape, and this one is substantial: 22 metres across and 3.5 metres high, its rounded profile now smothered in furze so that it resembles a natural hump of hillside rather than anything deliberately built. There are no visible kerbstones, the large upright slabs that typically ring and define such monuments, and the summit has a noticeable hollow where stone was removed at some point, probably quarried away by people who found a ready-made pile of building material on their doorstep.

The cairn sits within the townland of Ballinascorney Upper in south County Dublin, documented in detail by Healy in 1975. What has complicated its survival is less the passage of millennia than the pressures of the twentieth century. In 1994, the construction of a forest road cut directly into the northern, western, and north-western edges of the monument, a damaging intervention that removed part of the cairn's perimeter. Around the same time, or at some point since, both a metal pole and a wooden pole were inserted into the monument's edge on the north-western side, and a metal tripod was placed on the summit itself, presumably for surveying or telecommunications purposes. Forestry has since been planted right up to the south-eastern quadrant, pressing the trees close against the ancient mound.

The cairn is not signposted and reaching the summit of Tallaght Hill requires a walk through managed forestry, so a decent pair of boots and some patience with unmarked tracks are advisable. The furze covering the mound is dense, which means the scale of the structure is easier to appreciate from a short distance than from standing directly on it. The central hollow is visible from the top, and the tripod and poles make the summit straightforward to locate even when the mound's outline is obscured by vegetation. The townland boundary bend that aligns with the monument is not marked on the ground, but knowing it is there adds something to the experience of standing on what is, by any measure, a quietly ancient and somewhat battered piece of the Dublin uplands.