Its 71 gun loops in walls and 7-shape were intended to protect it from all sides. North Hoy Nature Reserve Windswept moorland and sea cliffs of this RSPB nature reserve make ideal habitat for hundreds of birds, from kittiwakes to Arctic skuas. Cliff formations include 450ft stack called Old Man of Hoy. North Ronaldsay Most northerly of isles of Orkneys is ringed by 6ft stone wall to protect crops from sheep. Sheep survive on seaweed yet produce fine wool.
Prehistoric fort remains on southern coast.
Two Mainland farmsteads show evolution of Orkney farm buildings over centuries. Kirbuster is the only surviving farmhouse with hearth in middle of floor. Corrigal's 19th-century house has gable fireplace and wooden box beds. Traditional breeds of sheep and poultry. Orphir Church Ruin of 12th-century circular Mainland church overlooks Scapa Flow's northern shore.