Jantar Mantar is a group of astronomical observatories built in the early 18th century by Maharaja Jai Singh II, a ruler of the Rajput kingdom of Amber, in what is now Jaipur, Rajasthan, India. The observatory at Jaipur is the largest and most well-known of the five observatories built by Jai Singh II and is home to the world's largest sundial.