The Saraswati (mythological/subterranean), Ganges, and Yamuna rivers are believed to unite at Prayag, now known as Allahabad (Prayagraj). This confluence, called Triveni Sangam, is one of the most sacred sites in Hinduism. The Ganges and Yamuna physically meet here, while the Saraswati is believed to flow underground. Options A, C, and D are major Indian cities but not this specific confluence site.