Living proof of the genius and passion of Sawai Jai Singh, this medieval observatory is the largest of its kind in the world, and the best preserved of Jai Singh's five observatories. There are 18 instruments in all, erected between 1728 and 1734 -- many of Jai Singh's own invention. The observatory looks more like a modern sculpture exhibition or sci-fi set -- hard to believe these instruments were constructed in the 18th century and remain functional. Some are still used to forecast how hot the summer will be, when the monsoon will arrive, and how long it will last. Whether or not you understand how the instruments are read (and for this, you should try to avoid coming on an overcast day -- almost all the instruments require sunlight to function), the sheer sculptural shapes of the stone and marble objects and the monumental sizes of many (like the 23m-high/75-ft. Samrat Yantra, which forecasts crop prospects based on "the declination and hour of the heavenly bodies") are worth the trip and make for great photographs (evidenced by the Indian visitors who like to pose atop many of them as if they were starring in some esoteric Bollywood blockbuster). After a major upgrade of the observatory in 2007, improvements now include more visitor-friendly explanations of how everything works; alternatively, hire a guide at the gate for Rs 100 to Rs 150, but you'll do far better booking Jaimini Shastri; be sure to book him well in advance. Tip: If you'd prefer a forecast of future events that are more focused on yourself, you could always call upon the renowned (and very important) Dr. Vinod Shastri, who practices palmistry, predictive dice-throwing (ramal), and computer-aided astrological predictions in an office just around the corner (Chandni Chowk, behind Tripolia Gate; tel. 0141/261-3338). A professor of astrology and palmistry at Rajasthan University, Dr. Shastri is available between noon and 7pm, but you should know that his asking fee ranges from Rs 600 to Rs 3,000 for a session lasting just 10 minutes.