This is the Seto inland sea which separates Shikoku island from the Japanese main island of Honshu. It wasn't until a tragic ferry accident in the 1980's that Japan undertook the massive task of establishing bridges from the main island to Shikoku island. Kurushima Kaikyo Bridge (shown) it is the first example of three linked suspension bridges in the world. They span the 4-km wide Kurushima Strait. The area around the bridge has several ship building facilities. The bridges are an engineering marvel. I've included this link to the bridge authority's web site.
Honshu-Shikoku Bridge Expressway Company Limited
