The cluster covers an area of approximately twenty metres east to west and twenty metres north to south, a mixture of granite, sandstone, and smaller quartz pieces, many of them water-rolled rather than quarry-fresh. That detail matters: water-rolled stones suggest the builders gathered material from a beach or riverbed, carrying it deliberately to this headland. Local tradition has long held that this is a burial site, and the flint retrieved repeatedly from the surrounding fields lends that tradition some weight. A miniature stone axe was also found in the immediate vicinity, reported by Kieran Campbell, and small ceremonial axes of this kind are occasionally associated with Neolithic funerary contexts.

A passage tomb is a type of megalithic monument, typically Neolithic in date, in which a stone-lined corridor leads to a central burial chamber, the whole structure usually covered by a mound of earth or cairn material. What survives at Knocknagin is less legible than that description implies, but the site appears on William Duncan's 1821 map of County Dublin, where it is marked simply as a 'moat', the term then commonly applied to any prominent earthwork or mound without much further distinction. The location itself is on a headland north of Lowther Lodge, a position that would have given the monument considerable visibility in the landscape, with open views northward along the coast towards the Mourne Mountains and southward to the Bremore tombs in County Meath, a cluster of passage tombs that form part of the same broader prehistoric coastal tradition.

The site sits in agricultural land and access requires care and awareness of farming activity, particularly given that the field is described as tillage ground. The stones are subtle rather than dramatic; a visitor unfamiliar with megalithic remains might walk past without registering what they are. The elevated position of the stone scatter within an otherwise stone-free field is the clearest indicator that something deliberate happened here. The coastal aspect means the surrounding landscape itself is part of what makes the place intelligible, and looking south towards Bremore on a clear day gives a sense of how these monuments were distributed and perhaps related across the shoreline.