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Snana yatra - bathing of Lord Jagannatha. The story is that the deity is bathed (on this ocasion everyone is allowed to come and bathe, touch the deity, normally only priests can do it).
Then Lord "catches cold" after so much bathing and goes to bed for 2 weks, when He is given a special medicine to get better, it made of mixed curd, cream, candy and butter with cinamon.
After He gets better we will have even a bigger festival, Ratha-yatra, Lord Jagannatha will go out of His temple (once a year ocasion) in a big cart with large wooden wheels pulled by people. He goes around streets and everyone can come and offer service to the Lord, even people who normally don't go to the temple, animals, etc - all are given darsan and mercy of the Lord on that day.