The Jantar Mantar is an equinoctial sundial, consisting of a gigantic triangular gnomon with the hypotenuse parallel to the Earth's axis. On either side of the gnomon is a quadrant of a circle, parallel to the plane of the equator. The instrument is intended to measure the time of day, correct to half a second and declination of the Sun and the other heavenly bodies.
There are five Jantar Mantars in India, of which the largest is in Jaipur which features many instruments along with the world's largest stone sundial. The Vrihat Samrat yantra is a sundial that can give the local time to an accuracy of 2 seconds. It is a UNESCO World Heritage Site.
9 am - 4:30 pm
More info about individual items http://www.rajasthantourism.gov.in/Destinations/Jaipur/JantarMantar.aspx
Address Jaipur, India
Coordinates 26°55'29.06" N 75°49'28.078" E