Craziest festival you've ever been to/heard of?

I've got some time off this summer (a couple of weeks in June) and am taking part in the Hyakumangoku festival here in Kanazawa, Ishikawa. It's basically a huge procession (several kilometers long!) of people dancing through the streets!!!
I fancy pushing the boat out this year and attending as many festivals as I can. Don't mind travelling to anywhere in Japan to witness some craziness.
Anyone got any bizarre experiences/recommendations?

Shonan area

Have you ever visited the Shonan area of Japan? It is quite lovely.
If you know some Japanese music, you may have heard of Keisuke Kuwata (Kuwata Band, Southern All-Stars). He is from Chigasaki.
In Chigasaki, there is a fun festival each July. This year I think it will be held on July 18. It is called the Hamaorisai and pretty fun. You must get up early to see them chuck the oﾂーmikoshi into the ocean. Along Yuzo-dori (a main street directly leading from the station to the ocean) are many small shops. The beach area is nice for bicycling and some like to surf.
I do not have enough posts to add links yet. But if you go to chigasaki-kankou.org - you can find additional info.
Another festival in this area that is fun is the Tanabata Matsuri. The one in Hiratsuka is pretty big. There is a large parade of street dancing, etc. and many stalls with food, games, etc. The decorations are very colorful and some are HUGE. Nighttime is also great because there is a lot of illumination.
The info for this festival is found on the city.hiratsuka.kanagawa.jp site if you look for Tanabata.
The festival this year is the 61st one and happens over July 8 - 10th.

Fantastic information. I did a couple of Youtube searches on these festival and the Hamaorisai looks crazy! Will spend a little time researching both of these, but great suggestions!
I YouTubed (If we can use "Google" as a verb, why not "YouTube"!!?) the Tanabata Matsuri too and saw a horde of marauding Japanese people scrambling to save the best position on the street to watch the fireworks.
Love seeing the usually serene, polite and socially aware Japanese throw it all out of the window for a second or too!!

In Sapporo of Hokkaido from June 8,There is "YOSAKOI-SORAN Festival ".
Official site
YOSAKOIソーラン祭り 公式ホームページ

TohokuTakizawa-mura, Iwate ,June 11
Chagu Chagu Umakko

Chagu Chagu Umakko is a horse festival in Iwate Prefecture, Japan. Held on the second Saturday in June, approximately one hundred horses with colourful fittings and bells parade between Sozen Jinja in Takizawa and Morioka Hachiman-gū.[1] 'Chagu Chagu' is an onomatopoeic expression for the sound made by the horse's bells.[2] In 1978 the festival was recorded as an Intangible Folk Cultural Property.[3] In 1996 the sound of the bells of the Chagu Chagu Umakko was selected by the Ministry of the Environment as one of the 100 Soundscapes of Japan.

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A festival of Tokyo of June.
Shinagawa-ku, Tokyo EBARA Shinto shrine TENNOU-SAI
From June 4.
Official site
荏原神社-三大祭り