Minatogawa Zuidō (湊川隧道), dug by hand through Kaige-yama and finished in 1901, is described by Hyogo Prefecture as Japan's first modern river tunnel. It carried the Minatogawa river for a century until 2000, and a residents' preservation group now opens it to the public.
Why it's unique
Hyogo Prefecture describes it as the first modern river tunnel in Japan. The public wording is "first", not "oldest", and that is the claim made here.
It is normally locked, because it is legally still a river channel, so walking its 600 m of brick vault is something you can only do on the preservation group's open days.
Before you go
It is 600 m of brick vault built after an 1896 typhoon breached the levee and killed 38 people, and the bricks were laid to shed water at speed, which you can see in the curve of the floor. The 1995 earthquake cracked the portal; the damage is still visible.
It is legally a river channel and normally locked, so the open days are the only way in; the preservation group also holds concerts and film screenings inside.
