Cornwall (Cornish: Kernow ) is a duchy in the south west of the United Kingdom. Lying west of Devon from which it is separated by the River Tamar, Cornwall is one of the more isolated and distinctive parts of the United Kingdom but is also one of its most popular with holidaymakers. Its relatively warm climate, long coastline, amazing scenery, and diverse Celtic heritage (combined with tales of smuggling, pirates and King Arthur!) go only part of the way to explaining its appeal.