The Jantar Mantar or Yantra Mantra is a collection of architectural astronomical instruments located in west central India. Built by Maharaja Jai Singh II of Jaipur in 1727 until 1734, it consist five location. Each site has multiple building of unique form and each building has a specialized function for astronomical measurement. The sites are: Delhi -Yantra Mantra (Delhi), Jaipur -Yantra Mantra (Jaipur), Ujjain, Mathura and Varanasi.
The city of Jaipur is located about 220 km south and west of New Delhi, in the State of Rajasthan. It was designed and built as a “new city” ca. 1727 by Jai Singh, and incorporated architectural and plan-ning concepts that were advanced for their time. The city is also home to the largest and most elaborate of the five ob-servatories, located just across from the Royal Palace.
how these buildings work? Read more here