Held every 12 years at 1 of 4 places in India, the Kumbh Mela lasts nearly 2 months and is considered to be an especially auspicious time to bathe in the holy river for purification from sin. In 2001, the last time the festival took place, more than 40M people gathered in an area smaller than 20 sq km. This year, the predicted number of visitors tops 100M.