The Kanmon Strait (関門海峡) is the stretch of water separating two of Japan's four main islands. On the Honshu side of the water is Shimonoseki and on the Kyushu side is Moji port, now part of Kitakyushu City.

The Kanmon Strait can be traversed in a number of ways, the oldest of which is the ferry. There is also a bridge which carries an expressway. By far the most used method is the Kanmon Tunnel which carries the Shinkansen, trains, cars and even pedestrians.