The wall is a relatively recent addition; the tomb beneath it is not. What sits on a west-facing slope near Ballyganner is a wedge tomb, a type of Neolithic or early Bronze Age megalithic burial chamber found mainly in the west of Ireland, characterised by its tapered, trapezoidal form, wider and taller at one end than the other. This one is roughly 4.2 metres long, widening from about 2 metres at the north-east to just under 3 metres at the south-west, and sits at the centre of a low circular mound some 14.5 metres in diameter. The Ordnance Survey mapped it as a cromlech, the older catch-all term for any large prehistoric stone structure, in both its 1842 and 1920 editions.

When the archaeologists Ruaidhrí de Valera and Seán Ó Nualláin examined the tomb in 1961 for their Survey of the Megalithic Tombs of Ireland, they found the construction surprisingly intact and precise. Each side of the chamber consists of a large limestone slab stood on its long edge, with the top edge deliberately flattened to support a capstone. The south-west end features two distinct closing stones: a tall blocking stone with finely dressed side edges, and a smaller overlapping doorstone partially covering a gap between the blocking stone and the north-west sidestone. Thomas Westropp, writing in 1909, had already noted what he described as small basins or cup marks on the upper face of fallen capstone fragments lying within the chamber, a detail that still awaits firm interpretation. The capstone itself, estimated at around 6.1 metres by 4.2 metres, had partially collapsed, though two large pieces remained resting on the west and south-west corners of the structure.

By 1997, when the site was inspected again, the remaining capstone fragments had become dangerously unstable and had fallen further into the chamber. The Office of Public Works intervened to reposition them, inserting a steel bar along their north-east edges to hold them in place. The tomb does not sit alone in this landscape: a cashel, a type of stone-walled enclosure typically associated with early medieval settlement, lies about 85 metres to the south, a further enclosure sits roughly 109 metres to the north-east, and a hut site is located around 80 metres to the north-north-west. The field system surrounding the tomb is itself classified as multiperiod, meaning the area has been continuously shaped and reshaped by human activity across many centuries, the wedge tomb being only its oldest surviving element.