Jantar Mantar

Vedh Shala or Jantar Mantar is located in the holy city of New Ujjain. It is an observatory built by Maharaja Jai Singh II in 1725 which consists of 13 architectural astronomy instruments. The observatory is one of the five observatories built by Maharaja Jai Singh II when he was governor of Ujjain.

Vedh Shala was constructed with the aim of measuring local time, altitude (of the place) and also to measure declination of the Sun, stars and planets and to determine eclipses. Motion, speed and properties of stars and planets were also recorded using several special instruments.

Reference: https://en.wikipedia.org/wiki/Ved_Shala