Court tombs, among the oldest megalithic monuments in Ireland dating to the Neolithic period, typically follow a recognisable pattern: an open forecourt at one end leads into a main gallery of burial chambers. Here at Lagan, the court and gallery that would normally anchor the whole structure are either gone or were never clearly built. What remains is a grass-covered trapezoidal mound, roughly 31 metres long and 11.5 metres wide, sitting just below the crest of a south-facing slope, with scrub growing over it and a set of displaced stone flags at the north-east end that may once have formed the shallow court.

Beyond those displaced flags, the picture becomes more puzzling. Two subsidiary chambers open to the north-west, and a third opens to the south-east, an orientation that itself runs counter to the usual arrangement. Further to the south-west, additional set stones suggest the outlines of more chambers, though no main gallery has been identified. In a typical court tomb, subsidiary chambers branch off from a central passage; here, those secondary spaces appear to exist largely on their own terms. Whether the main gallery was dismantled, robbed for building material over the centuries, or simply never completed is unclear. What the surviving stonework does confirm is that the monument belongs to the court-tomb tradition, with chambers comparable in form to the subsidiary sections found at better-preserved examples elsewhere in Ulster and the northern midlands.