The Jantar Mantar of Delhi, an early-18C astronomical observatory, was designed on the request of the emperor, by the founding maharaja of Jaipur, Jai Singh II. Its structures were so reliable that they made it possible to pick out mistakes in the astronomical tables of the greatest scholars of the day. Nowadays, though, surrounded by modern buildings, they are unusable but create a surreal sight. Note, in particular, the Samrat Yantra, a gigantic sundial.