Orkney also known as the Orkney Islands,is an archipelago in northern Scotland, 16 kilometres north of the coast of Caithness. Orkney comprises approximately 70 islands, of which 20 are inhabited.The largest island, known as the "Mainland" has an area of 523.25 square kilometres making it the sixth largest Scottish island and the tenth-largest island in the British Isles. The largest settlement and administrative centre is Kirkwall.The Mainland is the largest island of Orkney. Both of Orkney's burghs, Kirkwall and Stromness, are on this island, which is also the heart of Orkney's transportation system, with ferry and air connections to the other islands and to the outside world. The island is more densely populated than the other islands and has much fertile farmland.The island is mostly low-lying but with coastal cliffs to the north and west and two sizeable lochs: the Loch of Harray and the Loch of Stenness. The Mainland contains the remnants of numerous Neolithic, Pictish and Viking constructions. Four of the main Neolithic sites are included in the Heart of Neolithic Orkney World Heritage Site, inscribed in 1999.The other islands in the group are classified as north or south of the Mainland. Exceptions are the remote islets of Sule Skerry and Sule Stack, which lie 60 kilometres west of the archipelago, but form part of Orkney for local government purposes. In island names, the suffix "a" or "ay" represents the Norse ey, meaning "island". Those described as "holms" are very small.Orkney has an abundance of wildlife especially of Grey and Common Seals and seabirds such as Puffins, Kittiwakes, Tysties, Ravens, and Bonxies. Whales, dolphins, Otters are also seen around the coasts. Inland the Orkney Vole, a distinct subspecies of the Common Vole is an endemic.There are five distinct varieties, found on the islands of Sanday, Westray, Rousay, South Ronaldsay, and the Mainland, all the more remarkable as the species is absent on mainland Britain.The coastline is well-known for its colourful flowers including Sea Aster, Sea Squill, Sea Thrift, Common Sea-lavender, Bell and Common Heather. The Scottish Primrose is found only on the coasts of Orkney and nearby Caithness and Sutherland.Although stands of trees are generally rare, a small forest named Happy Valley with 700 trees and lush gardens was created from a boggy hillside near Stenness during the second half of the 20th century.The North Ronaldsay Sheep is an unusual breed of domesticated animal, subsisting largely on a diet of seaweed, since they are confined to the foreshore for most of the year to conserve the limited grazing inland.