Six miles from the ferry on Rousay, mighty Midhowe Cairn has been dubbed the 'Great Ship of Death'. Built around 3500 BC and enormous, it's divided into compartments, in which the remains of 25 people were found. Covered by a protective stone building, it's nevertheless memorable. Adjacent Midhowe Broch, whose sturdy stone lines echo the rocky shoreline's striations, is a muscular Iron Age fortified compound with a mezzanine floor. The sites are on the water, a 10-minute walk downhill from the main road.