Jantar-Mantar is located about a quarter of Kilometer south of Connaught Place. Jantar Mantar is one of the world's oldest astronomical observatories. It was built by Maharaja Jai Singh II of Jaipur along with 4 other observatories at Ujjain, Jaipur, Mathura and Varanasi. Apparently, he was much impressed with the works of Hindu and Islamic Astronomers and wanted to build an observatory to study these claims and findings.

The observatory consists of fourteen major geometric devices for measuring time, predicting solar eclipses, lunar eclipses, tracking stars movement, ascertaining the declinations of planets, cause of asteroids, determining the celestial altitudes and related ephemeredes. The only problem is that all of these are fixed, focused and immovable tools. The dominating buildings in the surrounding stop the sunlight and cast their own shadow.

The Samrat Jantar, the largest instrument, is 90 feet high. It's the largest clock in the world ever made. The shadow of this structure used to denominate time. Its face is angled at 27 degrees, the latitude of Jaipur. There is a cenotaph on the top of the Jantar, which was used to make special announcements such as solar and lunar eclipse and monsoon. All of the Jantar are built of local stone and marble. The scale of each Jantar is marked on that structure itself. Even the paths of the adjoining garden denote the orbits of various planets. Restored in 1901, the Jantar Mantar has been declared a national monument since independence.