The Kumbh Mela is one of the largest pilgrimages is the world; held over two months from January to March of every year.
It involves (literally) millions of Hindus gathering on the banks of four rivers: the Ganges, the meeting point of the Ganges, the Yamuna and the mythical Saraswati rivers, the Godawari and the Shipra.
The highlight of the event is bathing in the sacred waters of the river.
These rivers are located at Haridwar, Allahabad (also known as Prayag), Nasik and Ujjain.
The event rotates between every city every four years.
This year the event is at Allahabad and it’s the big one: it’s the Maha Kumbha Mela which is only held every 144yrs.
Here are some links to articles with lots of pictures: