This is a 780-meter-long undersea tunnel for pedestrians. The  undersea tunnel has two stories, the upper of which is a road for automobiles, and the lower for pedestrians. An elevator is installed at the entrance of the tunnel, so pedestrians go about 60 meters underground on the Moji-ku side or about 55 meters underground on the Shimonoseki City side before walking through the tunnel. At the middle of the tunnel is the sign of the prefectural border between Fukuoka and Yamaguchi Prefectures, famous as a rare example of an undersea prefectural border. If you affix commemorative stamps available in the elevator halls on both sides of the pedestrial tunnel, show these stamps at a tourist information center or other place, and answer a questionnaire, you can get a certificate of your surmounting "Kanmon" (also meaning "a hurdle").