The Maha Kumbh Mela ('Great' Kumbh Mela), happens after twelve (12) 'Purna Kumbh Melas', i.e. every 144 years.
Naturally, this mela is particularly significant due to the planetary positions at the time, a pattern that repeats only once every 144 years. The Maha Kumbh Mela is held at Prayag, and the last one was celebrated in 2001 and reportedly attended by approximately 60 million people.
A rarest of rare occasion, the Maha Kumbh Mela is naturally looked upon by most Hindus as a once in a lifetime occurrence that must be attended.
At the Maha Kumbh Mela, millions of Hindu devotees converge to take a ceremonial dip in the Triveni Sangam - the confluence of the three great rivers Ganga, Jamuna and Saraswati. It is accepted to be the spot where four drops of the sacred nectar had fallen during the battle between the Devas (demigods) and Asuras(demons) over the Amrit-Kumbh(pot of nectar). Attendees perform rituals and take a ritual bath. The bathing is done in the open with complete submersion of the body under water and performing an oblation to the sun.
Other important activities associated with the Maha Kumbh Mela include the singing of bhajans (devotional songs), discussions on religious matters, mass feeding of holy men and women and the poor, and gatherings where religious doctrines are debated and determined.
The next Maha Kumbh Mela is expected to take place in the year 2145.