Jantar Mantar - Pink City, Jaipur, India

Back in 1728, the rajah of Jaipur, Sawai Jai Singh II, sent emissaries out across the world to gather accurate astronomical data. On their return, Jai Singh ordered the construction of the Jantar Mantar complex in New Delhi. Made entirely from stone, and based on the astronomical tables of French mathematician Phillipe de la Hire, the monumental astronomical observatory was one of five observatories, with the largest in his hometown of Jaipur. The 73-ft sundial is the largest ever built.