Royal Observatory Greenwich, London

Designed by Christopher Wren, the Royal Observatory Greenwich was founded in 1675 to compute exact longitudes for navigational purposes. However, by 1948 London's glow had become too bright for star gazing, and the astronomers decamped to Sussex. Now the Old Royal Observatory is part of the National Maritime Museum . Discover the story of the search for longitude, the history of time and navigation, or stand on the line where east meets west and the point where the millennium started. Admission is free; some entrance fees may be charged for special exhibitions and events.