One of those graves, known to excavators as Grave 3, held the fragmentary remains of what was probably a young adult woman, her body originally laid on its right side in a contracted position, knees drawn up, facing east. The grave itself is a cist, a small stone-lined box built from upright slabs with flat capstones laid across the top, just 0.9 metres long, 0.5 metres wide, and 0.4 metres high. Modest in scale, it is the kind of construction easy to overlook against the broader drama of the cairn mound that surrounds it.

The cairn at Poulawack had already accumulated a long burial history before this cist was ever inserted. Radiocarbon dating places Grave 3 between approximately 1610 and 1432 cal BC, situating it within a final phase of mortuary activity at the site during the mid-second millennium BC, when at least one other burial was also added. The oval pit into which Grave 3 and its neighbour were set measured roughly 6.5 metres north to south, 4 metres east to west, and nearly 2 metres deep, meaning that those who dug it were deliberately reopening and reworking a monument that was already old. The excavation that brought all this to light was carried out in 1934 by the Third Harvard Archaeological Expedition in Ireland, led by Hugh O'Neill Hencken, who afterwards restored the cairn. The skeletal remains Hencken's team found within Grave 3 were disturbed and incomplete, so the details of the original burial arrangement are partly inferential, reconstructed from what survived of the bones and their positions on the cist floor.