North Ronaldsay

Seaweed-eating sheep are confined to the foreshore by a 13-mile stone dyke that encircles the entire island — the sheep eat kelp because the wall keeps them off the grass, and their digestive systems have evolved over centuries to process it. North Ronaldsay runs on traditions that would make no sense anywhere else.

North Ronaldsay is the northernmost island in Orkney, home to fewer than 50 permanent residents and a flock of sheep unique in the world. The sheep were confined to the foreshore by a stone dyke in the 19th century to protect the island's limited grazing land, and over generations their digestive systems adapted to a seaweed diet — a biological adaptation that makes them a subject of ongoing scientific study. The dyke itself requires constant communal maintenance, a tradition that defines island social life. Britain's tallest land-based lighthouse, the Old Beacon, flashes from the northern tip, and the island's breeding bird colonies include Arctic terns, skuas, and waders.