A stone observatory, part of the city palace complex, Jantar Mantar is one of several other astronomical observatories created by Maharaja Sawai Jai Singh 2nd (other are in Delhi, Banaras, Ujjain). These concrete masonry instruments were used to measure everything from altitude to time, and map the movement of the planets and the stars. Jai Singh 2nd had a passion for astronomy and used astronomical inventions from different of these observatories, the largest of which in is Jaipur.