The high-speed rail tunnel extends as far down the mountains as some of the deepest mines on the planet.

Nothing stands in the way quite like Europe's highest and most extensive mountain range.

With France on one end and Austria the other, the Alps sprawl 1,200km across eight countries in a massive crescent shape.

Historically, Alpine crossings were perilous journeys taken on foot or mule. For as long as people have been in Europe, they have sought to cross this mountain range so vital for travel, trade and war.

The Romans fought battles to control routes through the Alps. Historic figures, including Hannibal — with elephants in tow — then later Napoleon, led armies over the mountains to gain a strategic wartime advantage.

They'd have wished for something like the Gotthard Base Tunnel, a corridor between northern and southern Europe that opened in 2016. At the cost of about £11.5bn, it is the longest and deepest tunnel ever built.

It's a crucial link for travel as well as the transport of goods across Europe. Used by freight and passenger trains, it cuts travel time from Basel to Zurich and Milan to Lugano by up to an hour.

The Gotthard tunnel extends 57km — a 20 minute journey underneath the majestic Alps that loom above. Remarkably, its depth of 2.3km is comparable to some of the deepest mines in the planet.

Trains are able to zip through at a maximum speed of 155mph due to their clever design.

Where older tunnels spiral their way up the mountains, the Gotthard is completely flat. It's the first flat route through the Alps or any other mountain range.

As the world's longest tunnel, it bypasses the Channel Tunnel running between England and France by 7km.

It beat out the previous world record holder, Japan's Seikan rail tunnel, by 3km. The Seikan tunnel connects the country's two largest islands, Honshu and Hokkaido.

The tunnel was created to replace the first Gotthardbahn rail tunnel, an engineering marvel of its time that was completed in 1882.

Plans for its replacement began a century later in the 1980s. It was an ambitious and arduous project that took 17 years to build.

With 35 miles of mountain pressing down on the route, one of the critical challenges was how to prevent the tunnel from collapsing in on itself. Fortunately, reinforced steel rings spanning the tunnel support the weight of the mountain above.

The project required the use of a massive drill the length of four football fields. At 410m long and 10m wide, it carved through 40m of mountain a day.

The Daily Star  UK