The Snana Yatra is a bathing festival celebrated on the Purnima (full moon day) of the Hindu month of Jyeshtha. It is an important festival of the Jagannath cult. This is the first occasion in the year as per the Hindu calendar, when he deities Jagannath, Balabhadra, Subhadra, Sudarshan and Madan Mohan are brought out from the Jagannath Temple (Puri) and taken in a procession to the Snana Bedi. There they are ceremonially bathed and decorated for a public audience with the devotees.
It is a belief among devotees of Lord Jagannath that if they make a pilgrimage to see the deity on this day, they would be cleansed of all of their sins. Hundreds of thousands of devotees visit the temple on the occasion. The Skanda Purana mentions that King Indradyumna arranged this ceremony for the first time when the idols of the deities were first installed.
On the eve of the Snan Yatra (Which means the Bathing festival, in Sanskrit), the idols of the deities are brought out in a grand procession from the Garbhagriha (sanctum sanctorum) to the Snan Bedi (bathing platform). Devotees come to view the deities.
On the day of the Snana Yatra, the deities are bathed with 108 pots, made of gold, of ritually purified water drawn from the northern well of the temple to the accompaniment of religious incantations. In the evening, at the conclusion of the bathing ritual, Jagannath and Balabhadra are dressed up in elephant headgear representing the God Ganesh. This form of the God is called the 'Gajavesha'
After the Snana Yatra the Gods are traditionally believed to fall ill and are kept in a sick room to recuperate in privacy under the care of the Raj Vaidya. The Royal Physician of the king of Puri. It is said that with the Ayurvedic medication ('panchan') administered by the Raj Vaidya the Gods recover in a fortnight and resume giving an audience to their devotees.
On the full moon day of Jaista Purnima (Snana Purnima) the deities are decorated with beautiful Vesha known as Gajanana Vesha or Hati Vesha. There is a legend behind this Vesha. Sri Ganapati Bhatta a great devotee of Lord Ganesha from South India came to Puri to see Lord on the day of Snan Purnima. On the auspicious day he however could not see Lord Ganesha on the Snana Mandap. He was disappointed. But Lord Jagannath is great, He is antharyami, He could know the heart of His devotee. On order to appease the desire of Ganapati Bhatta, Lord manifested Himself in the form of Lord Ganesha. Since that day this Vesha is being observed on the day of Snana Purnima.