During the twelve-year battle between Gods and Demons for the nectar of immortality, Amrita, four drops of the elixir fell dwon to earth.
Today these are the cities of Allahabad, Haridwar, Ujjain and Nashik, in which the Kumbha (vessel) Mela (festival) is celebrated every twelve years.
Read about Kumbha Mela here
http://utkarshspeak.blogspot.com/2013/01/kumbh-mela.html
http://utkarshspeak.blogspot.com/2013/01/kumbh-mela-and-naga-babas.html
https://www.jagranjosh.com/general-knowledge/what-is-the-difference-between-naga-sadhu-and-aghori-baba-1550149886-1