A new, set to open in 2029 is expected to become the world's longest underwater rail and road tunnel. The major plan has been drafted to drastically reduce travel time between Scandinavia and Central Europe under the Baltic Sea.

The Fehmarn Belt fixed link, also known as the Fehmarn Belt tunnel, will transform the current 45-minute ferry crossing into a much quicker train journey, connecting southern with northern . This monumental tunnel will also play a significant role in the transport sector's shift towards greener solutions. Originally, the project was estimated to cost over £4.6 billion, but this figure rose to £6.2 billion in 2010 after the signing of the Denmark-German treaty to build the tunnel, as reported by German site Bund. The Danish government will finance the tunnel and recoup costs through tolls collected from the crossing.

Last year, Danish King Frederik X inaugurated the first segment of the future 11-mile tunnel. He revealed a plaque at the entrance of the initial 711-foot section.

The tunnel will establish a direct link from Roedby in Denmark to Puttgarten in Germany, providing onward connections by road and rail to central Europe and the Nordic countries. It will replace the heavily used ferry service currently run by Scandlines.

Sund and Baelt, the company responsible for building the link, has claimed this will be the longest submersible tunnel in the world.

Motorists will be able to cross the Baltic Sea in a mere 10 minutes on the four-lane route, while train journeys are expected to take just seven minutes.

The tunnel will also feature an electrified high-speed rail line, with trains reaching speeds of up to 125 mph.

Building is underway at what's been dubbed North Europe's largest construction site, located in Roedbyhavn on Lolland. The first of the 89 concrete elements needed for the project was cast in May last year.

Fehmarn is linked to the German mainland by the Fehmarn Sound Bridge, which opened in 1963. Lolland is connected to Zealand via a series of tunnels and bridges through the island of Falster. This is then linked to the Swedish mainland via the Øresund Bridge, which began construction in 1995 and was completed four years later.

The decision to connect the southern Danish island of Lolland with the northern German island of Fehmarn was made in 2011. Construction began on the Danish side in July 2022, followed by the German side a year later.

In 1998, a road link was established between the islands of Funen, home to Denmark's third-largest city, Odense, and Zealand, where Copenhagen is located. In 2000, a bridge-and-tunnel-link across the Oresund Strait connected Copenhagen to Malmo, Sweden's third-largest city.