Last year construction began on a new tunnel linking the Danish island of Lolland with the German island of Fehmarn, which then connects to the German mainland. The new tunnel replaces a time consuming ferry link or a very long round trip via Denmark’s Jutland Peninsula. Here's a video demonstrating how it is being constructed:
At 11 miles long, the tunnel will use the equivalent amount of steel to 50 Eiffel Towers and employ 3000 people during the 8.5 year build.
The way this tunnel is being constructed is what is interesting. Instead of boring under the seabed, like the Channel Tunnel between England and France, the Fehmarn Link will be constructed as 79 separate 711-foot long prefabricated elements, which will be floated out into the sea on a barge, and then submerged and placed in a trench that has been dug at the bottom of the sea.
For more amazing bridge and tunnel plans, read '9 New Massive Bridges and Tunnels That Could Unite Countries and Continents' here.