Seto Inland Sea (瀬戸内海 Seto Naikai) is a body of water separating Honshu and Shikoku, two of the main islands of Japan. Before the construction of the Sanyo Main Line, it was the main transportation link between the Kansai region and Kyushu.
Hiroshima prefecture, Yamaguchi prefecture, Okayama prefecture, Kagawa prefecture, and Ehime prefecture all have coasts on the sea. The cities of Hiroshima, Iwakuni, and Matsuyama are also located on the sea.