The Sarasvati originated in the Himalayas two thousand years ago and flowed into the Arabian Sea in Gujarat, on the border between India and Pakistan. Today it can no longer be identified as a river, but lives on as a mythological/mystical river.
In Allahabad, at Triveni Sangam, the visible rivers Ganga and Yamuna and the invisible Sarasvati meet. Allahabad is one of the most sacred pilgrimage destinations in India.
Read about Sarasvati here