Naked Festival

A hadaka matsuri hadakamatsuri (lit. naked festival) is a type of Japanese festival, or matsuri, where participants wear a minimum amount of clothing; usually just a Japanese loincloth (called fundoshi), sometimes with a short happi coat, and very rarely completely naked. Whatever the clothing, it is considered to be above vulgar, or everyday, undergarments, and on the level of holy Japanese shrine attire. Naked festivals are held in dozens of places throughout Japan every year, usually in the summer or winter.

Source: Wikipedia