NARRATOR: Three thirteen-year-olds from the UK are on their way to explore the geography of India ... the river end? MAP SELLER: Huh? DUA: Where does the river end? The Ganges.

Every twelve 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 Kumbh Mela, the largest gathering of humanity ...