Gotthard Base Tunnel in the context of "Lepontine Alps"

Altdorf (Swiss Standard German pronunciation: [ˈaltˌdɔrf] ) is a municipality in Switzerland. It is the capital of the Swiss canton of Uri and retains historic town privileges. It is the place where, according to the legend, William Tell shot the apple from his son's head.

Altdorf is situated on the right (eastern) bank of the Reuss, about 2 kilometres (1.2 mi) south of where the river discharges into the Urnersee, an arm of Lake Lucerne. It is at the junction of two major Alpine passes—Saint Gotthard to the south and the Klausen Pass to the east—and is the last station on the Gotthard railway before the line enters the Gotthard Base Tunnel, the world's longest railway tunnel.

The Gotthard Pass or St. Gotthard Pass (Italian: Passo del San Gottardo; German: Gotthardpass) at 2,106 m (6,909 ft) is a mountain pass in the Alps traversing the Saint-Gotthard Massif and connecting northern Switzerland with southern Switzerland. The pass lies between Airolo in the Italian-speaking canton of Ticino, and Andermatt in the German-speaking canton of Uri, and connects further Bellinzona and Lugano to Lucerne, Basel, and Zürich. The Gotthard Pass lies at the heart of the Gotthard, a major transport axis of Europe, and it is crossed by three traffic tunnels, each being the world's longest at the time of their construction: the Gotthard Rail Tunnel (1882), the Gotthard Road Tunnel (1980) and the Gotthard Base Tunnel (2016). With the Lötschberg to the west, the Gotthard is one of the two main north-south routes through the Swiss Alps.

Since the Middle Ages, transit across the Gotthard played an important role in Swiss history, the region north of the Gotthard becoming the nucleus of the Swiss Confederacy in the 13th century, after the pass became a vital trade route between Northern and Southern Europe. The Gotthard is sometimes referred to as the "King of Mountain Passes" because of its central and strategic location.

A ballastless track or slab track is a type of railway track infrastructure in which the traditional elastic combination of sleepers and ballast is replaced by a rigid construction of concrete or asphalt. It is considered the standard for high-speed and heavy-haul railway lines. It is also commonly used for urban tramways.

The Simplon Tunnel (Simplontunnel, Traforo del Sempione or Galleria del Sempione) is a railway tunnel on the Simplon railway 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 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, when the Daishimizu Tunnel opened.

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.

The Helsinki–Tallinn Tunnel (also known as FinEst or Talsinki tunnel) is a proposed undersea tunnel that would span the Gulf of Finland and connect the Finnish and Estonian capitals by train. The tunnel's length would depend on the route taken: the shortest distance across would have a submarine length of 80 kilometres (50 mi), which would make it 40% longer than the current longest railway tunnel in the world, the 57 km (40 mi)-long Gotthard Base Tunnel in Switzerland.

During the 2010s, it was estimated that the tunnel, if constructed, would cost €9–13 billion and could open in the 2030s if approved. In 2013, the European Union approved €3.1 million in funding for feasibility studies. A 2015 pre-feasibility study proposed trains traveling with a top speed of 250 km/h (155 mph). On 8 February 2024, Finnish Minister of Transport and Communications Lulu Ranne stated in an interview for Estonian newspaper Postimees that the tunnel is "unrealistic" and not on the government's agenda, with the project remaining on hold unless the European Union decides to allocate additional funding for it.

The Ceneri Base Tunnel (CBT; Italian: Galleria di base del Monte Ceneri) is a Swiss railway base tunnel in the canton of Ticino. It passes under Monte Ceneri between Camorino in the Magadino Flat and Vezia near Lugano; it bypasses the former high-altitude rail route through the Monte Ceneri Tunnel. It is composed of two single-track tunnels, each 15.4 km (9.6 mi) long. It is part of the New Railway Link through the Alps (NRLA) project for faster north-south rail links across the Swiss Alps.

An exploration tunnel near Sigirino was excavated between 1999 and 2003 to gain geological data on the rock formations at the Ceneri Base Tunnel's level. Based on those data, it was decided to excavate most of the tunnel with traditional blasting methods and only drill a small part using a faster tunnel boring machine (TBM). Both the CBT and Gotthard Base Tunnels were built under contract from the Swiss Federal Government by Alptransit Gotthard AG. Construction of the two single-track bores started during March 2006. The official start of the CBT's construction phase was celebrated on 2 June 2006 with the laying of a foundation stone. The final breakthroughs took place on 21 January 2016 (west tube) and 26 January 2016 (east tube). Rail service started on 4 September 2020 and was operationalised for freight in December 2020.