At 2,300 metres deep and 57 kilometres long, the Gotthard Base Tunnel broke records when it opened to traffic in 2016.

       The idea of making a new tunnel in the Swiss Alps to connect the North Sea and the Mediterranean train was first thought up in the 1960s.

       But it wasn't until 2012 that the huge project finally came to fruision and work began to construct a specially-designed straight tunnel that would allow trains to travel through at 250km/h.

       In order to build the tunnel millions of cubic metres of rock had to be excavated from beneath the alps, using huge tunnel boring machines known as "giant moles".

       READ MORE: New ￡24bn city being built for 11m people whose homes will be underwater

       The idea behind the tunnel was to give different parts of Switzerland an economic boost.

       Construction bosses from Ballast Nedham say the record-breaking structure has been able to cut the journey time between Zurich and Milan to just two hours and 40 minutes - saving an hour from before the structure.

       Once opened it also took the crown of longest traffic tunnel, at 57km, taking the crown from the Japanese Seikantunne.

       And, although it reaches staggering depth of 2,300m, the Gotthard Base Tunnel has only small height differences meaning it feels relatively flat.

       The Gotthard Base Tunnel

       Don't miss... Brits sent major warning about going into sea at 25 popular UK beaches [LATEST]

       Ballast Nedam says: "Since the tunnel opened, approximately 260 freight trains race through it every day. This freight traffic is a mode of transport that contributes to the Swiss national economy and the environment."

       And while the tunnel has now been operational since 2016, disaster struck in 2023 when a train derailed inside the structure.

       The tunnel itself received extensive damage and had to be closed following the incident on August 10. The initial derailment led to a further 30 wagons being derailed.

       It meant only one tube of the tunnel was allowed to reopen, with priority given to freight trains. However, the complete reopening of the tunnel is expected in September.