Jantar Mantar, Jaipur

Jantar Mantar is a collection of about twenty stone and marble instruments built by Sawai Jai Singh II in the 1720s, next to his palace inside the walled city. Nothing here has a lens. Each device is a piece of architecture sized so that a shadow or a sightline can be read to a fine tolerance: sundials, hemispherical bowls sunk into the ground, graduated arcs, and a separate instrument for each sign of the zodiac. The largest, the Vrihat Samrat Yantra, is a stair-like gnomon tens of metres high whose shadow moves fast enough to watch. The site is on the World Heritage list and makes far more sense with a guide than without one.

What you actually see

• Vrihat Samrat Yantra - the huge sundial whose shadow visibly creeps along a graduated marble arc.
• Jai Prakash Yantra - two sunken marble bowls mapping the sky, read from inside the hollows.
• The Rashivalaya - twelve separate instruments, one per zodiac sign, each set at its own angle.
• Ram Yantra - open cylindrical structures used to take altitude and azimuth readings by eye.

When to go

Late morning to early afternoon is when the instruments actually work, since most of them need direct sun; an overcast sky or a late arrival leaves half the site inert. October to March is bearable outdoors. Come at opening time if you want the yard without tour groups, and hire a guide at the gate rather than guessing.

Honest expectations

The site is a bare, unshaded courtyard and the Rajasthan sun is punishing from March onwards. Without explanation the instruments read as abstract concrete, and guide quality varies a lot; some rush through memorised patter. It is small, and the ticket is priced for the combined palace circuit rather than for the hour you actually spend here.

Nearby

The City Palace is next door and Hawa Mahal is a few minutes' walk up the bazaar.