Naruto Whirlpools 鳴門の渦潮
An exciting boat ride at Naruto no Uzushio!
These whirlpools, created in the straits of Naruto by different sea levels in the Inland Sea and in the Pacific Ocean, are particularly strong at the changing of the tide. Note: this is a lot more exciting than it may sound.
Surprisingly, normally risk-averse Japanese seem quite happy to hop on a sightseeing boat that drives right into the whirlpools and gets tossed about like a floating cork. Check the website for images and tide times.
Alternatively, walk the Uzu-no-michi viewing walkway that hangs beneath the Naruto Bridge and takes you out for views directly down on the whirlpools. Tide times are on the website.