Jantar Mantar Observatory was one of the five observatories constructed by Maharajah Jai Singh II between the years 1727 and 1734. This was built based on the one in Delhi. The name Jantar means instrument and Mantar means formula or calculation. This means the calculation instrument.

The Jantar Mantar Observatory has fourteen geometric devices that are used for measuring time, tracking the location of the stars and for calculating the declinations of the planets, etc. The largest instrument is Samrat Yantra which is 90 feet high. Its shadow tells the time. Though the instruments are huge in size they are placed in such a way to give accurate results.

Some of the instruments in the Jantar Mantar Observatory are Ram Yantra, Narivalaya Yantra, Jai Prakash Yantra, Rashivalaya Yantra, Kapali Yantra, Chakra Yantra, Laghu Samrat Yantra, etc. It is opened to public from 9 A.M. to 4.30 P.M.