The Jantar Mantar is a collection of architectural astronomical instruments, built by Maharaja Jai Singh II in Jaipur between 1727 and 1734. It is one of five such facilities he had constructed at different locations. The Jaipur observatory is the largest and best preserved of these. It has been inscribed on the World Heritage List as "an expression of the astronomical skills and cosmological concepts of the court of a scholarly prince at the end of the Mughal period". It consists of fourteen major geometric devices for measuring time, predicting eclipses, tracking stars' location as the earth orbits around the sun, ascertaining the declinations of planets, and determining the celestial altitudes and related ephemerides. Each is a fixed and 'focused' tool. The Samrat Yantra, the largest instrument, is 90 feet (27 m) high, its shadow carefully plotted to tell the time of day. Its face is angled at 27 degrees, the latitude of Jaipur.
When told I was going to be taken to visit an "observatory" this was not what came to mind - I expected something more modern and was delightfully surprised.