Explanation : Prayagraj, formerly known as Allahabad, is famous for hosting the Kumbh Mela every 12 years. The Kumbh Mela is one of the largest and most significant religious gatherings in the world, where millions of Hindu pilgrims gather to bathe in the holy rivers, primarily the Ganges (Ganga), Yamuna, and Saraswati (mythologically believed to converge at Prayagraj). The event is based on astrological calculations and rotates between four pilgrimage sites in India: Prayagraj, Haridwar, Ujjain, and Nashik. Each location hosts the Kumbh Mela once every 12 years, with Prayagraj being especially renowned for the massive scale and significance of the event.