Thousands of naked men come to the temple Saidai-ji in Okayama in Japan to the Hakada Matsuri or better known as the Naked Festival every third Saturday in February.
They appear nearly naked, wearing only fundoshi, traditional undergarment for men. The crowd rushes into the temple in order to grasp a pair of wooden sticks and some little holy things which mean luck for the period of one year.
The tradition is very old and archaic.
There are some videos on youtube to get an impression.
And a very good explanation on the blog oddityjournal.com plus some detailed photos.