The cairn is 38m long, 19.5m wide and 3m high. The original 9.1m long entrance passage is in the centre of the east-south-east side of the cairn. It is now closed: the chamber is reachable through a hatch in the roof and a ladder.
Within the huge cairn is a very long main chamber (its total length is 20.4m). At either end of the chamber there is an extension, divided from the main part by cross-walls with low lintelled doorways.
Twelve side-cells (two of them double) open off the main chamber. Eleven stones of the chamber bear pecked decoration (zig-zags, circles, inverted Vs, dots and arcs). The best decoration, ornamented with hollows and 'eyebrow' motifs, is on the lintel of the entrance of the last south-east side-cell.
No artefacts or human bones were found when the tomb was excavated in 1849.
At the opposite end of the islet is another, much smaller chambered cairn known as Holm of Papa Westray North.
In care of Historic Scotland