However, a lot of people don’t realize that it’s possible to walk between the islands as well using the Kanmon Pedestrian Tunnel which runs between Shimonoseki City in Yamaguchi Prefecture (Honshu) ...

(drumroll here): the Kanmon Straits. It’s a body of water ... The sea can be crossed by a toll expressway bridge, tunnel, Shinkansen, local train, ferry and, I was intrigued to learn, on foot.