St Kilda (Scottish Gaelic: Hiort) is an isolated archipelago situated 64 kilometres (40 mi) west-northwest of North Uist in the North Atlantic Ocean. The largest island is Hirta whose sea cliffs are the highest in the United Kingdom. The Gaelic-speaking population probably never exceeded 180 in number and was never more than 100 after 1851. Although St Kilda was permanently inhabited for at least two millennia and had a unique way of life, the local population was evacuated in 1930. The islands continue to be administratively a part of the Western Isles of Scotland.
They are a breeding ground for many important seabird species including Northern Gannets, Leach's Petrels, Atlantic Puffins, and Northern Fulmars. The St Kilda Wren and St Kilda Field Mouse are endemic sub-species.
The entire archipelago is owned by the National Trust for Scotland and became one of Scotland's four World Heritage Sites in 1986, and is one of the few in the world to hold joint status for its 'natural', 'marine' and 'cultural' qualities.
Parties of volunteers work on the islands in the summer months to restore the numerous and unique ruined buildings the native St Kildans left behind. They share the island with a small military base which was created in 1957.