Travelling the 11 miles between the Danish town of Rødbyhavn and the German town of Puttgarden involves either a 45-minute ferry journey – plus time for embarking and disembarking – or a six-hour drive taking in large parts of Denmark.

However, when the Fehmarnbelt tunnel opens in 2029, people will be able to cross the stretch of water in seven minutes by train and 10 minutes by car.

The new tunnel is seen as the final stage of a three-part project – alongside the Øresund Bridge and the Great Belt Bridge, which links to the Danish islands of Zealand and Funen – connecting Denmark, and the Nordics as a whole, with the rest of Europe. Once the tunnel is completed, it will be possible to transport goods, including steel, by rail from as far north as the top of Norway to central and southern Europe. It will cut the train journey time between Copenhagen and Hamburg from 4.5 to 2.5 hours.

It symbolises the culmination of a transformation of the Danish psyche over the past quarter of a century, from a relatively isolated peninsula and collection of islands to an international hub.

“It’s part of this link which Europe is trying to make between northern Norway and southern Europe, which started when we built the Øresund Bridge between Copenhagen and Malmö,” Mikkel Hemmingsen, chief executive of the state-owned company Sund & Baelt, said. “To finish the link, we have to build this connection.”

Unlike a lot of tunnels that run underwater – including the Channel tunnel – which have been constructed using boring machines that burrow under the ground, sections of the Fehmarnbelt tunnel are being built above ground and submerged on to the sea floor. Hemmingsen said this approach was more efficient and better for the environment.