Three sacred rivers meet at Allahabad: The Ganges, born of clear Himalayan tributaries that first trickle and then rage down from India’s border with Tibet; its sister, the Yamuna, which shadows the Ganges to the west before curving past Delhi and the Taj Mahal to join her; and the mythical Saraswati, ancient and invisible, which is said to run beneath the earth.

Only the Saraswati reaches Allahabad in a pristine state.

My latest, at National Geographic.