At "Strait and History Town: Shimonoseki" which is surrounded by ocean on three sides, "Shimonoseki Kaikyo Marathon" is held every year on Sunday early November. About 120 million runners will be gathering from inside and outside of the country, and they compete the time enjoying the beautiful scenery along the ocean. There are three events: full marathon, 5km, and 2km. For full marathon, you start from Kaikyo Messe Shimonoseki, go eastward along the the Inland Sea for Kanmon Bridge, go back and go up north through Hikoshima Island which is on the southern tip of Yamaguchi. On the road, there are many points that crossing the ocean such as Kangen-Kyo Bridge and Hikoshima Bridge. At the 27km point, you cross the Choshu Dejima Bridge which is arched over an offshore artificial island and you cannot go through usually so it is a valuable course.
For the details, please go to the official HP below.