This is Jantar Mantar, which is a 200 year old observatory that Jai Singh II built. He basically sent a whole bunch of smart people to the ends of the World to study astronomy, and then they came back to build this observatory.It has the largest sundial in the World that is accurate to 2 seconds. The thing stands at least 100 meters tall. They also have a whole bunch of interesting contraptions to measure the altitude of the sun or something like that.
