The Ohara Hadaka Matsuri (大原はだか祭り, “Ohara Naked Festival”) is a 2-day annual festival held in Isumi City, Chiba. On the Saturday, half-dressed men carry portable shrines through the town and towards the local fishing harbour, before making a lot of noise and tossing them as high as they can in the air. The most photographed spectacle, however, is the shiofumi (汐ふみ)—a procession that sees each mikoshi (portable shrine) carried into the sea one after the other. On the Sunday there is also a procession of the mikoshi around the town, but it’s Saturday that obviously attracts the biggest crowds. If you plan on going, aim to get to the harbour area for around midday.
Despite the distance from Tokyo and its location on the east coast of the Boso Peninsula, Ohara isn’t too difficult to reach. The Wakashio Limited Express from Tokyo Station gets you there in about 70 minutes (direct) for just under ¥3,000.