It has been 30 years since the Channel Tunnel, linking France and England, opened to the public, but it could soon be set to be joined by another underwater tunnel in Europe as construction has recently begun on one underneath the Baltic Sea. 

The Chunnel, as it is sometimes referred to, is 31.5 miles long, with 23.5 miles being underneath the English Channel. Subsequently, it is the longest underwater tunnel in the world. 

It runs between Calais in northern France and Folkestone in Kent, which is the route people travelling by car use. However, it also services passenger-only trains between London St Pancras and Paris. 

The idea of connecting the two countries originated as long ago as the early 1800s, and experimental tunnels started to be built in the late 19th Century. They even used boring machines to get the project up and running, but construction properly began on the current version in 1988. 

There are three tunnels linking the UK to France that run parallel to each other; the first being one for passengers to France from England, the second for those travelling the other way, and the third is a service tunnel. They were built below the seabed and are 75 metres below sea level at the deepest point. 

However, the Eurostar is not going to remain the only European underwater tunnel for much longer, as another one is being built between Germany and Denmark. 

The route will stretch 11.2 miles underneath the Baltic Sea and will be known as the Fehmarnbelt tunnel. 

According to New Atlas, it is hoped it will be the longest immersed tunnel in the world, which means it will be built off-site and then immersed in the water. Designers also anticipate it will become the world’s deepest tunnel that can take both road vehicles and trains. 

It is expected to be complete by 2029 and, once operational, it will link Rodbyhavn in Denmark with Fehmarn in Germany. This will mean those wanting to travel between the two will only have to face a ten-minute drive or a seven-minute train journey across the Baltic Sea. 

Currently, the ferry takes 45 minutes between the two locations. 

The tunnel is expected to cost DKK 8.4 billion, which equates to £950.4 million, with the construction requiring 360,000 tonnes of rebar, 373 football pitches as the build site, and 70 vessels. Around 12 million cubic metres of soil has already been dug from the seabed to allow the construction of the tunnel to get underway. 

It will feature 79 standard sections, each weighing 73,000 tonnes and being 217m long, 42m wide and 10m tall. There will also be ten other sections, which are wider and taller, but not as long.

The tunnel sections will be submerged into the sea and positioned on the seabed at 40 metres below sea level. 

King Frederik X of Denmark recently opened the first section of the tunnel, which is expected to be sunk into position soon.