Which country is linked to Switzerland by the Simplon Tunnel?

The Simplon Tunnel is a railway tunnel on the homonymous line that connects Brig, Switzerland and Domodossola, Italy, through the Alps, providing a shortcut under the Simplon Pass route. It is straight except for short curves at either end. It actually consists of two single-track tunnels built nearly 15 years apart. The first to be opened is 19,803 m (64,970 ft) long; the second is 19,824 m (65,039 ft) long, making it the longest railway tunnel in the world for most of the twentieth century, from 1906 until 1982, before a longer tunnel was finally opened 76 years later.

Culminating at a height of only 705 m (2,313 ft) above sea level, the Simplon Tunnel was also the lowest direct Alpine crossing for 110 years, until the opening of the Gotthard Base Tunnel in 2016. The tunnel has a maximum rock overlay of approximately 2,150 m (7,050 ft), also a world record at the time. Temperatures up to 56 °C (133 °F) have been measured inside the tunnel.

Work on the first tube of the Simplon Tunnel commenced in 1898. The Italian king Victor Emmanuel III of Italy and the president of the National Council of Switzerland Ludwig Forrer opened the tunnel at Brig on 10 May 1906. The builders of the tunnel were Hermann Häustler and Hugo von Kager. Work on the second tube of the tunnel started in 1912 and it was opened in 1921.