At the entrance to the City Palace is Jantar Mantar, the 'Yantralaya' of Sawai Jai Singh II, the last great classical astronomer in India. The modernistic structures known as 'Yantras' are the unique creations of this astronomer-king designed by him and built by experts to observe the movements of sun, moon, planets and the stars.

This is the largest of five observatories founded by him in 1716 AD. The others are at Delhi, Ujjain, Mathura & Varanasi. Its massive masonry instruments are of an extraordinary precision & can still be used to measure local time, the sun's declination, azimuth & altitude, the declination of fixed stars & planets & also to determine the time of an eclipse of the sun