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... The project's main construction site is located at the northern entrance to the tunnel, on the coast of Lolland island in the south east of Denmark.

The facility spans more than 500 hectares (1,235 acres), and includes a harbour and a factory that is manufacturing the tunnel sections, which are called "elements".

"It's a huge facility here," says Henrik Vincentsen, chief executive of Femern, the state-owned Danish company that is building the tunnel.

To make each 217m (712ft) long and 42m wide element reinforced steel is cast with concrete.

Most underwater tunnels - including the 50km Channel Tunnel between the UK and France " burrow through bedrock beneath the seafloor. Here instead, 90 individual elements will be linked up, piece by piece, like Lego bricks.

"We are breaking records with this project," says Mr Vincentsen. "Immersed tunnels have been built before, but never on this scale." ...

[map is in the article]