Jantar Mantar is an astronomical observatory located in Jaipur, the capital city of the Indian state of Rajasthan. It is one of the largest and best-preserved observatories in the world. Jantar Mantar was built by Maharaja Sawai Jai Singh II, who was a Rajput king and a keen astronomer.

The Jantar Mantar in Jaipur consists of a collection of architectural and astronomical instruments, designed to observe and measure various celestial phenomena. The observatory features 19 main instruments, including the Samrat Yantra (the world's largest sundial), the Jaiprakash Yantra (a massive hemisphere used for measuring the position of celestial bodies), and various other yantras (instruments) for measuring time, altitude, azimuth, and other astronomical parameters.