In middle ages, there weren't many astronomical modern tools or observatories that we see today. So basically Jantar Mantar was an astronomical observatory of the Rajputana empire. This was specifically used for research purpose. This observatory was mainly used to measure the distance or positionsat an instance of time of planets and other celestial bodies.
This beautifully constructed marvel consists of 19 main instruments. These 19 instruments serves for different purpose. Jantar Mantar became for its Samrat Yantra, which is said to be the largest sundial in India. This architectural marvel has jaipurian architectural design. This beauty was constructed by Raja Sawai Jai Singh 2. It is said that the king was quite intrigued by such things and so constructed this place. Now this place brims with tourists throughout the year. This is a must place to visit if you are planning to visit Jaipur.