Walk to an island on a path the tide reveals
In a few places in Japan, a strip of sand or rock rises out of the sea at low tide and joins the shore to a small island, so you can walk across and back. The path appears for only a few hours, and on some days not at all, so look up the day's low tide before you go. Start back in good time, because once the tide comes in you cannot walk back.
A sandbar on Shodoshima, an island in the Seto Inland Sea, appears for a few hours around low tide and links the beach to a chain of small islets. Locals say couples who cross hand in hand will stay together, so many people walk it in pairs. Times change every day and are posted by the island's tourism association, and Shodoshima is about an hour or less by ferry from Takamatsu.
On the west coast of the Izu Peninsula, a sandbar runs from the beach out to Sanshiro-jima, a cluster of small rocky islands, when the tide is very low. You can walk across and peer into tide pools among the rocks, with the sea cliffs of Dogashima behind you. It does not appear at every low tide, so check the tide table on the Nishiizu town website, and wear shoes that can get wet.
Enoshima is usually reached by a long bridge, but on days of a very low tide a strip of sand appears beside it, and you can walk over from Katase Beach. In the daytime this happens only on some days of the year and lasts about two hours, so check the calendar on the Fujisawa tourism site. The island has shrines, sea caves and a lookout tower, and it is a little over an hour from Tokyo by train.
A line of tall rock pillars marches out to sea at Kushimoto, on the southern tip of the Kii Peninsula. At low tide you can pick your way across the rocks to Benten-jima, a small island partway along the line, about a 30-minute round trip from the roadside rest area. The way is over slippery rocks rather than sand, so wear shoes with good grip.