Unst is one of the North Isles of the Shetland Islands, Scotland. It is the northernmost of the inhabited British Isles and is the third largest island in Shetland after the Mainland and Yell. It has an area of 46 square miles (120 km2).Unst is largely grassland, with coastal cliffs. Its main village is Baltasound, formerly the second largest herring fishing port after Lerwick and now the location of a leisure centre and the island's airport.