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Fuji-Hakone-Izu NP, Shizuoka
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Dogashima’s sea-road is built by waves and revealed by the tide: Sanshiro-jima bends and weakens incoming waves, so calmer waves meet and pile stones into a bar. Shizuoka designated it a Natural Monument in 1983.
This crossing is made of large and small stones, not soft sand. At low tide, the bar stretches about 220 m and reaches up to 40 m wide; locals have long called this stretch of coast Sehama.
The islets preserve magma pathways from an ancient submarine volcano. As the magma cooled, it cracked into column-shaped joints; on Zojima, those patterns trace a profile that looks uncannily like an elephant.
These waters are tengusa country: the Izu Geopark says Japan’s largest agar-seaweed catch comes from seas that include this one. In Nishiizu, the red algae becomes tokoroten jelly—a homemade treat and former candy-shop staple.
The island group has 4 named islets, yet from some viewpoints it looks like only 3. Local guides point to this three-or-four optical trick as the explanation for the name Sanshiro-jima.
At the lowest tides, the exposed sea-road becomes a chain of temporary aquariums. The Environment Ministry reports tide pools where fish and crustaceans can be seen; local guides also find sea slugs and tiny fish among the seaweed.
Local legend says Genji warrior San-shiro hid on Nakanoshima during the Genpei era. Koyuki, daughter of a local clan leader, tried to cross the tideway with a message for him—but the incoming tide swept her away.
A verse in the local Dogashima Kouta warns lovers to cross Sehama at ebb tide: when the water rises, their feelings cannot reach the other shore. The disappearing path became part of the area’s romantic folklore.
At a 2016 Tombolo-opening event, participants cleaned the shore, then formed a human line to pass a giant “346” balloon along the exposed route to the island. Food stalls served local Kaizoku-yaki and shiokatsuo udon.
