Jantar Mantar in Jaipur is an astronomical observatory and one of the most significant historical landmarks in India. It is a UNESCO World Heritage Site and a brilliant example of Indian architectural and astronomical expertise during the 18th century. Built by Maharaja Jai Singh II in 1728, Jantar Mantar is located near the City Palace in the heart of Jaipur. It features a collection of architectural astronomical instruments used for measuring time, predicting eclipses, tracking stars, and determining celestial events.