Among the many rituals and traditions related to Onam, the journey of the 'Thiruvonathoni' is a spectacular one. The 'Thiruvonathoni' is special - it is almost like a snakeboat but with a Garuda-face on the prow. It is launched a couple of days before Onam and contains food items, which will be used for the grand Onam feast at Aranmula Temple on Thiruvonam day.
There is an interesting legend behind this. The Bhattathiri of Kattoor Madam used to offer Onasadya to a brahmin every year. One year, however, no one turned up. Deeply saddened by this, the Bhattathiri prayed to Lord Parthasarathi at Aranmula and soon, a small boy came and ate the sadya. He also told the Bhattathiri that it would be better to offer the Onamsadya at the temple itself.
The Bhattathiri did as directed. And over years, around 18 other families in the region joined in and now, it is a festival for the entire area.
As is the custom, the 'Thiruvonathoni' will set sail from Kattoor Maha Vishnu Temple on Uthradom day after the evening pujas are over and reach Aranmula early on Thiruvonam day. A grand feast follows and thousands join the celebrations. The festivities will end on Uthrattathi day with a snakeboat race.