Every 12 years, tens of millions of men, women and children gather on the flood plain of the Ganges and Yamuna Rivers in Allahabad, India, for the world's largest gathering for religious purposes. This is the Kumbh Mela, the great Hindu festival when pilgrims bathe where two sacred rivers meet. Such mass bathing has been recorded for more than 2,500 years. Feiler travels to the Kumbh with a group of spiritual seekers from across America. After surviving an out-of-season monsoon that floods much of the Mela camp, they meet with some of India's leading spiritual gurus and join millions of fellow pilgrims in a ritual that Hindus believe washes away sins and breaks the endless cycle of reincarnation.