The Royal Observatory is home to time and space and is in Greenwich. Both the Prime Meridian of the world and London’s only planetarium are found here. Within the dome of the museum is the largest refracting telescope in the country. The galleries hold the original marine chronometers. These were special clocks designed to work at sea and enabled seamen to work out their longitude – their distance east or west of a set meridian. Being an Observatory originally, it was built on a hill. Your breathlessness on walking up the path to get there will be rewarded with some of the best views that London has to offer.