Jantar Mantar

An eighteenth-century astronomical observatory built by Jai Singh II, holding nineteen instruments constructed in masonry and marble rather than metal. He built them at architectural scale because brass instruments of the day were not precise enough at the sizes then possible — so the instruments here are the size of buildings, and several are still accurate. It was inscribed by UNESCO in 2010.

Yes. The Vrihat Samrat Yantra is the largest stone sundial in the world, with a gnomon about 27 metres high, and it reads local solar time to roughly two seconds. The shadow moves fast enough to watch — around a millimetre a second across the quadrant — which is the detail most visitors remember. It obviously needs sun, so an overcast day removes much of the point.

More than at any other site in Jaipur. There are nineteen instruments and almost no interpretation on the ground, so without an explanation the observatory reads as a yard of strange ramps and bowls. Guides are available at the gate and an hour with one turns the site from puzzling into remarkable. It is the difference between seeing it and understanding it.

It adjoins the City Palace in the old walled city and the Hawa Mahal is a short walk through the bazaar, so the three are normally done together in a morning. A composite ticket covers several Jaipur monuments and pays for itself if you are visiting more than one. Amber Fort, a few kilometres north, is usually a separate half day.