Many Hindus are familiar the story of sagar Manthan or the churning of the ocean. Once Indra lost his kingdom due to the disrespect he showed to sage durvasa. The helpless Indra rushed to Vishnu for help.
Vishnu had a plan. He said that the gods would have to churn the oceans and bring out the magical nectar- amrita to get back their powers. After that they regain their powers. This great churning is known as Sagar Manthan. But as the gods were powerless now and they sought to help of demons to accomplish of huge task.
The god and demons got together to for the huge task. Mandara, the huge mountain was used as the pole to stir the waters. But as the pole entered the water it kept sliding into the depth of the ocean. To stop this, the lord Vishnu transformed himself to the tortoise and placed the mountain back and the tortoise was second avatar of Vishnu called ‘kurma’.
Once the pole was balanced, it was tied to the snake, vasuki, and the one side gods and the other side demons started pulling it. As the churning began and the massive waves whirled, an extremely poisonous drink came out called halahal and the blue drink could destroy creation. So, they all got together and prayed to the powerful Shiva to help him them then bholenath appeared before all and drank the entire poison. But he did not swallow it and kept the poison in his throat. So this reason that the throat of Shiva became blue and he became known as neelkantha.
The churning continued and poured forth a number of gifts and treasures. They included kamdhenu, the wish to fulfilling cow; the goddess of wealth Laxmi, the wish to fulfilling tree, kalpavriksha; and finally, came dhanwantari carrying the pot of amrita and a medicine called ayurveda. Once the amrita was out, the demons forcefully took it away. Rahu and Ketu are the demons, disguised themselves as gods and drank amrita. The sun and moon gods has to be a trick and complained to Vishnu, who in turn, severed their heads with his sudarshan chakra. As the divine nectar did not get time to reach below the throat, the heads remain immortal, but the body below died. It takes revenge of helps the both rahu and ketu, on the sun and moon by devouring them every year during solar and lunar eclipse.
A great war between the gods and demons then finally, lord Vishnu, as mohini tricked the demons and recovered the nectar. While fleeing the clutches of the demons, Vishnu gave the amrita to garuda. But the demons caught up and followed a tussle. During this tussle few drops of the drink fell at Ujjain, Nasik, Allahabad, and Haridwar.
The drops are said to have purified the land and every year devotees come to wash away the sins in the famous assembly called kumbh mela.
Once garuda got back then the gods drank the nectar and became immortal. But some demons had managed to taste a few drops of the drink, they too became immortal and the fight between good and evil continues to this day.