The Kanmon Straits (関門海峡 Kanmon-kaikyō?) or the Straits of Shimonoseki is the stretch of water separating two of Japan's four main islands. On the Honshu side of the water is Shimonoseki (下関, which contributed "Kan" (関) to the name of the strait) and on the Kyushu side is Kitakyushu, whose former city and present ward, Moji (門司), gave the strait its "mon" (門). The straits silt up at the rate of about 15 centimetres per annum, and dredging has made it possible to build the New Kitakyushu Airport at low cost.
The total population of the Kanmon area is about 1.3 million, counting the whole of Kitakyushu (approx. one million) and Shimonoseki (approx. 300,000), although detailed definitions vary widely (see Fukuoka–Kitakyushu). The New Kitakyushu Airport opened in Kitakyushu on March 16, 2006, and is expected to bring further prosperity in the form of increased tourism and trade to the area.
The Kanmon Straits Summer Fireworks Festival is held in August every year.
The Voyager pleasure boat departs from Moji-kō and cruises the straits.
Helicopter joyrides are available from Kaikyo Dramaship in Moji-kō.
In October 2005, one of the world's largest airships currently flying (a Zeppelin NT imported from Germany) also passed through Moji on an all-Japan tour. This airship was purchased by Nippon Airship Corporation in June 2004 and was used in the Tokyo area and at the Aichi Expo 2005.