A strait town of whirlpools and sea bream
Naruto, at the northeastern tip of Shikoku facing Awaji Island, sits on a narrow strait where the tide rushes through so fast that it spins the sea into whirlpools. Look straight down at them through a glass floor in a walkway under a bridge, then eat local sea bream (tai), said to be firm from swimming in the fast water, as sashimi or over rice. It is about two hours from Osaka by highway bus, so it works as a day trip; the whirlpools are biggest around high and low tide, so check the tide table first.
Stand on glass 45 meters above the sea and watch the whirlpools churn right below your feet. They come and go as the current shifts, so stay a while to see several. The tide table on the official English site shows when they are biggest, around high and low tide.
A restaurant inside Naruto Park, a short walk from the walkway, where you eat tai-don, slices of local sea bream marinated in sauce over rice, looking out at the strait and the bridge. It makes an easy lunch right after the whirlpools.
A local diner whose set meal serves wild sea bream three ways: as sashimi, simmered in sweet soy, and cooked into rice. It is in town rather than at the strait, so stop on your way back toward the station. It is closed on Wednesdays.
A museum of about 1,000 Western masterpieces reproduced at full size on ceramic panels, including a whole chapel recreated so you can stand inside it. It is next to Naruto Park, so it suits a rainy day or a wait for the tide, but seeing everything takes half a day. It is closed on Mondays.