February 15th is Saidai-ji Eyo Hadaka Matsuri

A Hadaka Matsuri (裸祭り "Naked Festival") is a type of Japanese festival, or matsuri, in which participants wear a minimum amount of clothing; usually just a Japanese loincloth (called fundoshi), sometimes with a short happi coat, and rarely completely naked.

Naked festivals are held in dozens of places throughout Japan every year, usually in the summer or winter. The most famous festival is the Saidai-ji Eyo Hadaka Matsuri held at Saidaiji Temple in Okayama, where the festival originated. Every year, over 9,000 men participate in this festival  in hopes of gaining luck for the entire year.