Blessed by a mild climate and bucolic surroundings, Torquay on the southern Devon coast proclaims itself the English Riviera. Its palm-lined waterfront warrants the name, and it is indeed one of England’s most popular resorts. Agatha Christie was born and lived here, and you can follow the plaques and pathways of the Agatha Christie Mile to learn about her life and work. The Kent’s Cave Prehisto…