Here's an announcement from the Kumamoto City International Foundation:
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■Ushibuka Haiya Dancing Festival
You can see more than 5,000 people dancing in the street.
Time period: Fri., 17th. ~ Sun., 19th. Apr.
Place: Ushibuka Haiya Bridge Glass Park, Ushibuka-machi shopping street, Ushibuka General Center, and so on.
Admission fee: free
Access: JR Kumamoto Station → Hondo Bus Center (about 2 hours by bus)
Hondo Bus Center → Ushibuka Port (about 1 hour by bus)
For more information: Ushibuka Haiya Planning Committee Office
(TEL: 0969-73-2111) *Japanese only
Website: http://www.city.amakusa.kumamoto.jp/
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The image you see and explanation in Japanese can be found at