Seikan Tunnel in the context of Hakodate, Hokkaido

Hokkaido (Japanese: 北海道, Hepburn: Hokkaidō; pronounced [hok.kaꜜi.doː] , lit. 'Northern Sea Circuit'; Ainu: Aynu Mosir, lit. 'Land of the Ainu') is the second-largest and northernmost of Japan's four main islands. Together with its surrounding islands, it comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu. The two islands are connected by railway via the Seikan Tunnel.

The largest city on Hokkaido is its capital, Sapporo, which is also its only ordinance-designated city. Sakhalin lies about 43 kilometres (27 mi) to the north of Hokkaidō. To the east and northeast are the Kuril Islands, which are administered by Russia. The four most southerly are claimed by Japan. Hokkaido's position on the northern end of the Japanese archipelago results in a colder climate, with the island seeing significant snowfall each winter. Despite the harsher climate, it serves as an agricultural breadbasket for many crops.

The Tsugaru Strait (津軽海峡, Tsugaru Kaikyō) 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.

Western maps made prior to the 20th century also referred to this waterway as the Strait of Sangar.

Hokkaido (Japanese: 北海道, Hepburn: Hokkaidō; pronounced [hok.kaꜜi.doː] , lit. 'Northern Sea Circuit'; Ainu: Aynu Mosir, lit. 'Land of the Ainu') is the second-largest and northernmost of Japan's four main islands. Together with its surrounding islands, it comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaido from Honshu. The two islands are connected by railway via the Seikan Tunnel.

The largest city on Hokkaido is its capital, Sapporo, which is also its only ordinance-designated city. Sakhalin lies about 43 kilometres (27 mi) to the north of Hokkaido. To the east and northeast are the Kuril Islands, which are administered by Russia. The four most southerly are claimed by Japan. Hokkaido's position on the northern end of the Japanese archipelago results in a colder climate, with the island seeing significant snowfall each winter. Despite the harsher climate, it serves as an agricultural breadbasket for many crops.

The Toei Ōedo Line (都営地下鉄大江戸線, Toei Chikatetsu Ōedo-sen) is a rapid transit railway line of the municipal Toei Subway network in Tokyo, Japan. It commenced full operations on December 12, 2000; using the Japanese calendar this reads "12/12/12" as the year 2000 equals Heisei 12. The line is completely underground, making it the second-longest railway tunnel in Japan after the Seikan Tunnel.

On maps and signboards, the line is shown in magenta. Stations carry the letter "E" followed by a two-digit number inside a more pinkish ruby circle.

The Tōhoku Shinkansen (東北新幹線) is a Japanese high-speed Shinkansen rail line that runs through the more sparsely populated Tōhoku region of Japan's main island, Honshu. Operated by the East Japan Railway Company, it links Tokyo in the south to Aomori in the north, with stops in population centers such as Morioka, Koriyama, Fukushima, Hachinohe, and Sendai. With a route length of 674.9 km (419.4 mi), it is Japan's longest Shinkansen line. It also has the highest operating speeds on the Shinkansen network, reaching a maximum of 320 km/h (199 mph) on a 387.5 km (241 mi) section between Utsunomiya and Morioka.

The first section of the Tōhoku Shinkansen opened in 1982 between Ōmiya and Morioka, with additional sections gradually built over the following decades; the final section between Hachinohe and Shin-Aomori was completed in 2010. A continuation of the line opened as the Hokkaido Shinkansen in 2016, which links Shin-Aomori to Shin-Hakodate-Hokuto via the Seikan Tunnel. The Tōhoku Shinkansen also has two Mini-Shinkansen branch lines, the Yamagata Shinkansen and Akita Shinkansen. Future plans include ongoing upgrade work to increase operating speeds throughout the line.

The Tsugaru Peninsula (津軽半島, Tsugaru Hantō) is a peninsula in Aomori Prefecture, at the northern end of Honshū island, Japan. The peninsula projects north into the Tsugaru Strait separating Honshū from Hokkaidō. The western coast is on the Sea of Japan, while on its eastern coast are Aomori Bay and Mutsu Bay. The peninsula is bisected from Cape Tappi at its northern end to the Hakkōda Mountains on its southern end by the Tsugaru Mountains. Across the Tsugaru strait to the north is Hokkaidō's Matsumae Peninsula, to which it is linked by the Seikan Tunnel.

The Hokkaido Shinkansen (北海道新幹線, Hokkaidō Shinkansen) is a Japanese high-speed Shinkansen rail line that links up with the Tōhoku Shinkansen in northern Aomori Prefecture in Honshu and continues on into the interior of Hokkaido through the undersea Seikan Tunnel. Construction started in May 2005; the initial Shin-Aomori to Shin-Hakodate-Hokuto section opened on 26 March 2016. The section of the line to Sapporo was originally scheduled to open by fiscal year 2030, but in December 2024 it was delayed until the end of FY2038, distressing local communities and causing concern over impact on regional development. The line is operated by the Hokkaido Railway Company (JR Hokkaido).

41°22′28.16″N 140°17′13.2″E / 41.3744889°N 140.287000°E / 41.3744889; 140.287000

The Kaikyō Line (海峡線, Kaikyō-sen) is an 87.8 km (54.6 mi) railway line operated mainly by the Hokkaido Railway Company (JR Hokkaido). The line connected Naka-Oguni Station in Sotogahama, Aomori, through the Seikan Tunnel between Honshu and Hokkaido, to Kikonai Station in Kikonai, Hokkaido. Two stations on the Tsugaru-Kaikyō Line, Tappi-Kaitei Station and Yoshioka-Kaitei Station (both closed since 2014), were inside the tunnel.

The Hokkaido Railway Company (北海道旅客鉄道株式会社, Hokkaidō Ryokaku Tetsudō kabushiki gaisha) is one of the constituent companies of the Japan Railways Group (JR Group), and is often referred to by its official abbreviation: JR Hokkaido (JR北海道, Jeiāru Hokkaidō). It operates intercity and local rail services in Hokkaido, Japan. The company introduced Kitaca, a smart card ticketing system, in autumn 2008.

At the time of its privatization in 1987, JR Hokkaido operated 21 railway lines totalling 3,176.6 kilometres (1,973.8 mi) of narrow-gauge (1,067 mm (3 ft 6 in)) track, as well as a ferry service to Aomori. Since then, that figure has dwindled to just below 2,500 kilometres (1,600 mi), as unprofitable lines have been shut down or spun off (in the case of the Hokkaidō Chihoku Kōgen Railway). The ferry service has also been replaced by the 53.85-km long dual-gauge Seikan Tunnel for railways.