The Brenner Base Tunnel is currently under construction and will connect the countries of Austria and Italy. The impressive tunnel, which is set to be the longest in the world, is scheduled to open in 2032.

The railway tunnel will connect the cities of Innsbruck, Austria, and Franzensfeste/Fortezza, Italy, linking two countries in different time zones. The construction costs are estimated at 8.54billion euros (£7.4billion). The impressive BBT will be a modern railway tunnel running for a total of 55km (34 miles).

BBT said: "In May 1994, a railway bypass was opened south of Innsbruck, known as the Inn valley tunnel. This 12.7 km tunnel links to the Brenner Base Tunnel.

"Passenger and freight trains along this stretch will therefore not only travel through the Brenner Base Tunnel, but for a few kilometres, through the Inn valley tunnel as well. This line, totalling 64 kilometres, will become the longest underground railway connection in the world."

A peculiar feature of the Brenner Base Tunnel is the "exploratory tunnel running from one end to the other".

"This tunnel lies between the two main tunnels and about 12m below them and with a diameter of 5m is noticeably smaller than the main tubes.

"The excavations currently underway on the exploratory tunnel should provide information on the rock mass and thereby reduce construction costs and times to a minimum.

"The exploratory tunnel will be essential for drainage when the BBT becomes operational." Other unusual railway constructions include the world's longest train journey, which connects three countries crossing eight time zones.