is a collection of architectural astronomical instruments built by Maharaja Jai Singh II ........

Explanation:

Jantar Mantar is located in the modern city of New Delhi. It consists of 13 architectural astronomy instruments. The site is one of five built by Maharaja Jai Singh II of Jaipur, from 1723 onwards,revising the calendar and astronomical tables. There is a plaque fixed on one of the structures in the Jantar Mantar observatory in New Delhi that was placed there in 1910 mistakenly dating the construction of the complex to the year 1710. Later research, though, suggests 1724 as the actual year of construction. Its height is 723 feet (220 m).