The is a strait between Honshu and Hokkaido in northern Japan connecting the Sea of Japan with the Pacific Ocean. It was named after the western part of Aomori Prefecture. The Seikan Tunnel passes under it at its narrowest point 12.1 miles (19.5 km) between Tappi Misaki on the Tsugaru Peninsula in Aomori Prefecture, Honshu, and Shirakami Misaki on the Matsumae Peninsula in Hokkaido.