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.

The others are at Delhi, Ujjain, Mathura and Varanasi. It's massive masonry instruments are of an extraordinary precision and can still be used to measure local time, the sun's declination, azimuth and altitude, the declination of fixed stars and planets and also to determine the time of an eclipse of the sun.