Onam is the harvest festival of Kerala. This festival is celebrated for 10 days. And the 10th day of this festival is celebrated as Thiruvonam or Onam. On 2022 Onam is celebrated on September 7. Festival starts from August 30.

History
The great king who won all three world Mahabali Chakravarthy was kind hearted and wise King. Although he is good king but he is demon. So all other God felt insecure and asked Mahavishnu to defeat the king. Mahavishnu agreed and took his Fifth avathar as The VAMANAN.
Vamana is the avatar where Mahavishnu looks like dwarf Brahmin. He visited as Vamana on before King Mahabali . The king promised to fulfil the wishes of Vamana. So Vamana asked to give him three piece of land. Vamana grew in big size. With one leg he covered sky and with other leg he covered the earth. Now he asked for third feet as king told to keep his feet on his head. When Mahavishnu kept his third step to his head , the king was defeated. Lord Vishnu gave him a boon that on every onam Mahabali chakravarthy is allowed to see his people and give his blessings.
Way of the Celebration:
As per the above story people believe that King Mahabali will visit their house at every Onam. They decorate the house and surrounding with flowers. They draw rangoli with flowers. They also prepare 26 dishes served on banana leaves called Onam Sandhya and celebrate with family members.
People also enjoys
Onakalikal ( Games played during the festival)
Vallamkali – Boat race
Pulikali- Tableau with actors dressed as Tiger and Hunters
Archery