That name alone signals something worth pausing over. Cú Chulainn is one of the great heroes of Irish mythology, and his name attaches to landscape features across Ireland, usually places that seem too large or too strange to have been made by ordinary human hands. A mound of stone nearly 23 metres across and 5 metres high, on a windswept hilltop, is exactly the kind of thing that invites such an explanation.

The cairn is the larger of two that stand roughly 1.6 kilometres apart along the same east-west ridge, which also marks the old parish boundary between Killiney and Ballinvoher. A disused wall running directly to the north of the cairn traces that boundary still. The original structure was more compact, perhaps 15 metres in diameter, but centuries of weathering and spreading have pushed the cairn material 3 to 5 metres beyond its drystone retaining wall, short sections of which survive at the east and west sides to a height of about a metre. A broad depression, 6 metres across, sits in the summit of the mound, and a smaller pit beside it is thought to be the scar of an old attempt to open the cairn and examine its contents. What, if anything, was found is unrecorded. Extending eastward from the cairn for roughly 200 metres is a meandering line of at least 16 upright or prostrate stones, orthostats and fallen slabs, decreasing gradually in size from west to east. Whether these formed a boundary feature or were part of the original monument is an open question. The tallest stone, at the western end of the row, carries a small cross carved into its south face, a detail that adds one more layer of ambiguity to an already complicated site, suggesting that someone, at some point, found the stone significant enough to mark.