Circular in plan and round-topped, it measures roughly six and a half metres across and stands between two and two and a half metres high, with kerbstones still visible along its eastern and south-western edges. A cairn of this form would ordinarily suggest prehistoric origins, a burial monument of the kind found across the Irish uplands, but here the picture is complicated by a single surveying detail that changes everything.

A trigonometrical station is marked at this point on Kilrock, and there is a real possibility that the cairn was not ancient at all but was built specifically to serve as a survey marker. Trigonometrical surveys, which use a network of fixed elevated points to calculate distances and map terrain with precision, became a major undertaking across Ireland from the early nineteenth century onward, and high, prominent summits were exactly the kind of locations that surveyors sought out. Whether a pre-existing mound was adapted for that purpose or whether the whole structure was raised as part of a mapping exercise remains uncertain. The shattered stone scattered across the surface could reflect great age, or it could reflect the practical, unsentimental approach of surveyors who needed something visible and stable rather than something beautiful.

The cairn sits on the Howth Head cliff path, which is well walked and straightforward to reach from the village of Howth itself, accessible by DART from Dublin city centre. The summit position means the views are genuinely wide, with Ireland's Eye, the small island just off the northern shore of the headland, sitting clearly in sight, and the coastline stretching away to the east. The kerbstones are easiest to read if you walk the full circumference of the mound rather than approaching from one direction. The site is unenclosed and open year-round, though the path can be exposed in poor weather.