I see barely clothed men run in my head... They run, compete for something, soak in the cold water even in winter. Of course there are many different types of Japanese festivals.
Tamatori-sai, known as Tamaseseri, is an annual Shinto ritual held at Hakozakigu Shrine, Fukuoka Prefecture on January 3rd. It dates back to 500 years. Two groups compete for a sacred wooden ball, which is believed to bring good luck to those who touched it.