Massive undersea tunnel to connect Denmark and Germany

A monumental engineering project is underway that will reshape the transport landscape of Europe. The Fehmarnbelt Tunnel, an undersea structure connecting Denmark and Germany, is poised to become the world’s longest road and rail tunnel, as well as the longest "immersed" tunnel ever constructed.

At 18 kilometres (11.2 miles), the Fehmarnbelt Tunnel will carry two lanes of road traffic and two electrified rail lines beneath one of the world’s busiest shipping lanes. Unlike traditional tunnels that are excavated through solid earth, the Fehmarnbelt will be constructed using prefabricated concrete sections that are floated to the seafloor, linked together, and submerged in a trench.

The project is set to drastically cut travel times between Denmark and Germany, reducing a 45-minute ferry ride to just 10 minutes by car and 7 minutes by train. The tunnel will halve the current travel time between Hamburg and Copenhagen, making it a game-changer for both passenger and freight transport.

Currently under construction with an estimated cost of €7.4 billion ($7.7 billion), the Fehmarnbelt Tunnel is a colossal undertaking. The first precast concrete sections, known as "elements," were recently completed in February 2025 at a factory in Rødbyhavn, Denmark, marking a key milestone.

These giant tunnel sections are 217 metres long, 42 metres wide, and 9 metres deep, each weighing an astounding 73,000 tonnes – the equivalent of 10 Eiffel Towers.

Construction of the tunnel’s portals at Rødbyhavn and Puttgarden is progressing, with the goal of completing the project by 2029. The tunnel is expected to not only enhance transport efficiency but also foster greater tourism, offering visitors more convenient access to the Scandinavian region.

Mads Schreiner, International Market Director at VisitDenmark, anticipates a boost in self-drive tourism, weekend getaways, and eco-friendly travel options like cycling and train tourism.

However, the massive project is not without environmental concerns. Despite several legal challenges related to its environmental impact, Femern A/S, the Danish company overseeing the project, is committed to mitigating any adverse effects. The company has already begun creating new natural areas, such as wetlands and grasslands, to offset the environmental footprint.

Once completed, the Fehmarnbelt Tunnel will not only be a marvel of engineering but also a pivotal link in European transport infrastructure, fundamentally changing how people and goods move across the continent.