The palace Man Mahal, popularly known as Man Mandir is located adjacent to the famous Dashashvamedh ghat hardly five kilometres from Varanasi railway station. Man Mahal situated on the western bank of river Ganga just adjacent to the famous Dashashvamedh ghat at Varanasi is a beautiful example of Mughal-Rajput architecture with stone balconied windows and painted ceiling. It is famous specially for its masonry observatory. The palace was built in around 1600 A.D. by Man Singh, the Raja of Amber and a celebrated General of the Great Mughal Emperor Akbar. But the observatory was added to it in around 1737 A.D by Sawai Jai Singh II (1686-1745 AD) who himself was a great astronomer, the founder of Jaipur city and a descendant of Raja Man Singh. Besides inventing a number of instruments, tables and formulae, constructed five masonry observatories located at Delhi, Jaipur, Ujjain, Varanasi and Mathura. These are popularly known as Jantar Mantar which is a corrupt form of Yantra- Mantra meaning thereby the calculation with the help of instruments.
The plan of the observatory in the palace of Man Mahal was prepared by Jagannath, an astronomer and the work was executed by an architect from Jaipur named Sardar Mohan under the supervision of Sadashiva. .Samrat Yantra (Small and large) Digamsa Yantra, Nadivalaya Yantra, Chakra Yantra and Dakshinottara Bhitti Yantra are the main instruments of this observatory. These are meant for calculating time, preparing lunar and solar calendar and studying the movements, distances, angles of inclination of the stars, planets and other heavenly bodies. By the orders of Maharaja Sawai Madho Singh of Jaipur, Pandit Gokul Chand Bhavan, the then court astronomer had carried out major restoration work to this observatory in the year 1912 as it was turned into ruins during the middle part of 19th century A.D.