A portal-tomb, sometimes called a dolmen, is a megalithic burial monument typically consisting of two or more upright stones capped by a large horizontal slab. Here the cap alone measures 3.25 metres by 2.3 metres and is 0.85 metres thick, a substantial piece of stone resting against an orthostat just 1.45 metres high. An inclined slab to the south may be a sillstone, a threshold element that would once have closed off the tomb's entrance. What makes this particular ruin remarkable, however, is not its form but what is carved into it.

The monument was first brought to wider attention by Conwell, writing between 1864 and 1866, who noted cup-shaped marks on the upper surface of the roofstone. He and subsequent commentators acknowledged that these might simply be the result of weathering rather than deliberate carving, and that is now the more likely explanation. The incised decoration on the underside of the roofstone and on the inward-facing side of the upright is a different matter entirely. Those markings are clearly intentional, though their context proved difficult to pin down and generated considerable debate among nineteenth and early twentieth-century antiquarians, including du Noyer in 1868, Borlase, Atkins in 1896, and Tempest in 1939. Writing in the same year as Tempest, Raftery argued that two of the curvilinear designs, including one featuring a triskele motif, a three-armed spiral symbol associated with Iron Age artistic traditions, were Iron Age in date, a view that still holds some weight. The remaining designs, mostly simple circles, connect more readily to the carved art found in passage tombs of the Boyne valley, suggesting that this single battered structure carries decoration spanning, or at least drawing on, more than one prehistoric tradition.

Because the most significant art is on the underside of the roofstone and the inward face of the upright, it is not visible without getting close to the stone and looking into the gap between them. The tomb sits on a slope, which affects both the angle of approach and the light, and the north-west orientation means afternoon or evening light may help pick out the incised lines more clearly than flat midday sun.