Spanning 18 kilometres (11 miles) of water with two double lane highways and two rail tunnels, it will reduce the journey from Hamburg to Copenhagen by half, from 5 hours to just 2.5 hours.

Credits: Getty Images; Author: Alina Rudya/Bell Collective;

Each 700-foot-long section of the tunnel weights as much as 10 Eiffel Towers, with 79 in total, and another 10 special sections that will house the largest electrical components.