Jantar Mantar  (Yantra - instruments, mantra - formulae) was constrcted in 1724. Maharaja Jai Singh of Jaipur who built this observatory went on to build other observatories in Ujjain , Varanasi and Mathura. Jai Singh had found the existing astronomical instruments too small to take correct measurements and so he built these larger and more accurate instruments.

The instruments at Jantar Mantar are fascinating for their ingenuity, but accurate observations can no longer be made from here because of the tall buildings around.