Set back from the road in steep slope, Blackhammer is one of 15 chambered cairns in Rousay and was first excavated in the 1930s. This 5000-year-old site is today entered by a ladder, but it originally featured a low, narrow entrance passage and a long central chamber with seven separate stalls. A wall was installed across the middle of the cairn at some point, reducing the accessible space, but the cairn is still full of interesting features.

There's decorative stonework, with stone slabs carefully arranged for a dramatic visual effect, similar to patterns found on incised stones across other Neolithic sites in Orkney.

The excavations found two adult male skeletons as well as fragments of animal bone, a bone pin, pottery and a polished stone axe.