IT IS one of Europe’s grandest feats of engineering and it’s been almost 70 years in the making.

But the Gotthard Base Tunnel in Switzerland — the longest and deepest railway tunnel in the world — is, at long last, mere days from being unveiled to a waiting world. The 57km tunnel, which will be opened on June 1, runs under the Swiss Alps and is expected to slash travel times across the heart of Europe. The concept for the tunnel was first sketched in 1947 but construction only started 17 years ago. Since then, about 28.2 million tonnes of mountain rock have been excavated — about enough to build five Pyramids of Giza — at a depth of about 22.9km. Overall, the ambitious project is estimated to have cost about $AU16.5 billion. “They have been boring through really hard rock,” former geotechnical engineer Claire Smith told NBC News. “This isn’t like a (subway) line running a few meters below the surface. “We’re talking depths that are measured in kilometres. Working down there is like going down a mine, it gets warmer as you go further in.” By overcoming a natural barrier to travel — mountain ranges — the Gotthard Base Tunnel is expected to shave travel time between Zurich and Milan down to two hours and forty minutes. That’s about an hour quicker than the trip currently takes by rail. And it could be a more viable alternative to air travel. EU transport commissioner Violeta Bulc said it was “a godsend for Europe”. The tunnel, “will be a vital link connecting Rotterdam (and) Antwerp with the ports of the Adriatic,” Bulc told Swiss media this week. It will make north-south travel more fluid, curb air pollution and “will be a driver of growth in Europe,” the Slovenian national was further quoted as saying. German Chancellor Angela Merkel, French President Francois Hollande and Italian Prime Minister Matteo Renzi, along with Swiss officials, are due to attend the grand opening next week. A series of test runs are scheduled for the coming months, with full service starting in December. It will also displace Japan’s 53.9km Seikan tunnel as the world’s longest train tunnel, and bump the 50.5km Channel Tunnel that links England and France into third place. But Austria’s delayed Brenner Tunnel could slot into second place when it opens in about a decade at an estimated length of 55km.