'Masterpiece of engineering' - Europe's new £6.4bn tunnel about to become world's longest

Stretching over an incredible 11 miles and crossable in just seven minutes, this tunnel is not only set to become the world's longest immersed tunnel, but it will also be the longest combined road and rail tunnel. Located under the Baltic Sea, the tunnel will connect two European countries, linking the Danish island of Lolland with the German island of Fehmarn. The Fehmarnbelt tunnel is the largest infrastructure project Denmark has ever seen and is set to be fully completed by 2029.

Construction on the tunnel started in 2020 on the Danish end and in 2021 on the German side of the tunnel, according to Femern A/S, which is the Danish state owned company that is in charge of building the tunnel. The tunnel will carry both trains and cars, creating a crucial link between Scandinavia and mainland Europe.

The journey between Rødbyhavn in Denmark and Puttgarden on the island of Fehmarn will only take seven minutes by train and 10 minutes by car.

As of July 2025, significant progress has been made on both the Danish and German sides of the Fehmarnbelt tunnel. The first onshore sections of the portal tunnel, connecting the future motorway and railway tracks to the underwater tunnel, are now complete in both countries.

On the Danish side, construction of the tunnel portal's light attenuation zone has also been finalised. This section includes an integrated light grid in the ceiling, designed to provide a smooth visual transition from daylight to the artificial lighting inside the tunnel.

The dredging of the tunnel trench, completed in 2024, produced nearly 15 million cubic meters of soil, sand, and stone. This material is being reused to develop around 300 hectares of new natural and recreational landscapes near Rødbyhavn.

Although the German construction site is smaller in scale than the Danish site, it plays a key role in the overall project. Work is being carried out in carefully phased stages, synchronised with the progress being made on the Danish side.

The German portal consists of two main parts with a 450-meter cut-and-cover tunnel and a 150-meter light transition zone. Both are designed in order to ensure a seamless connection to the motorway and railway systems on land.

Inland, two of the three new bridges required for the realigned route to the tunnel have been completed. Preparations for the third bridge are currently underway. The entire construction area spans the size of approximately 300 football fields.

Henrik Vincentsen, Chief Executive of Femern, said: "We are breaking records with this project. Immersed tunnels have been built before, but never on this scale."