The correct answer is Two. Key Points Udaipur and Allahabad, these two places he did not erect Astronomical observatories. Astronomical observatories at five places Delhi Banaras Jaipur Ujjain Mathura Additional Information About Astronomical observatories - The Jantar Mantar appears like a gallery of modern art. It is, however, an observatory. Sawai Jai Singh II of Jaipur (1699-1743), a keen astronomer and a noble in the Mughal court was dissatisfied by the errors of brass and metal astronomical instruments. Delhi's Jantar Mantar is the first of the five observatories that he built with large masonry instruments. The observatory has the Samrat Yantra, a simple equal hour sun-dial, the Ram yantra for reading altitudinal angles, Jai Prakash for ascertaining the position of the sun and other celestial bodies, and the Misra Yantra which is a combination of four scientific gadgets. Under patronage from the emperor, he set on himself the task of correcting the existing astronomical tables and updating the almanac with more reliable instruments.