The Seto Inland Sea (˓C, Setonaikai) lies between the Japanese main islands of Honshu, Shikoku and Kyushu. Its calm waters stretch over 400 kilometers from Osaka to Kitakyushu and include some 3000 islands, many of which are inhabited.

The Seto Inland Sea's mild climate and its islands' relaxed atmosphere invite comparisons with the Mediterranean Sea. Most of the sea is part of the Setonaikai National Park, one of the first national parks designated in Japan.

Historically an important trade route, the inland sea continues to be a vital shipping lane and is covered by an extensive ferry network, as many of the islands are connected to one another by small local ferries. The sea is also crossed by three major series of bridges that connect Honshu with Shikoku: the Shimanami Kaido between Hiroshima and Ehime, the Seto Ohashi Bridge between Okayama and Kagawa and the Akashi Kaikyo and Naruto Ohashi bridges between Tokushima and Hyogo.

Some islands in the Seto Inland Sea offer attractive resorts with beaches and other attractions. In particular, the eastern islands around Naoshima have become known as contemporary art destinations with several excellent museums on Naoshima, Inujima and Teshima. The Setouchi Art Festival is held every three years in this area. Other popular sightseeing spots around the Seto Inland Sea include the Shimanami Kaido and Miyajima.