Four Jantar Mantar survive (Mathura’s was demolished), but the one in Jaipur, completed in 1734, is the biggest and most comprehensive. Today, it is a Unesco World Heritage site, not only because it"s the best-preserved observatory of its kind in India, but as the Unesco inscription explains, it represents innovations in architecture, astronomy, and cosmology, as well as learnings and traditions from Western, Middle Eastern, Asian, and African cultures.