関門海峡
The carries National Route 2 under the Kanmon Straits. At the time of its construction, it was the longest undersea road in the world. It opened in 1958. The overall length is 3,461 meters, and it is 58 meters below sea level at the deepest point. The endpoints are in Shimonoseki, Yamaguchi and Moji-ku, Kitakyūshū.