Mousa, Shetland Islands, Scotland, UK

This tiny island, set just off Scotland’s southeast coast, is dominated by its eponymous broch, one of the country’s best-preserved prehistoric monuments. A unique Scottish phenomenon, brochs or fortified round towers represent the apex Iron Age dry-stone wall construction. Hundreds of these windowless towers once peppered northwest Scotland; of those that remain, the Mousa broch stands as the finest and most famous, mentioned twice in Norse sagas. Built around 300 BC and boasting 16-foot-thick walls, the 43-foot-high broch offers commanding views across Mousa Sound. Today the island is uninhabited – except, that is, for some 12,000 pairs of breeding storm petrels, one of the United Kingdom’s largest colonies. (Many nest inside the broch.) It also offers refuge for great skuas, Arctic terns, black guillemots and other seabirds, as well as seals and otters.