Norway is planning to build a submerged road tunnel underneath a fjord.
The ambitious project, which will cost £30 billion, will mean the construction of huge cylinders to carry cars under the body of water.
The tunnel will have two tubes for each direction of traffic and they will be anchored to both sides of the Sognefjord inlet.
The floating tubes will be attached to pontoons spaced about 800ft apart.
Because the fjord is 4,000ft deep, engineers are unable to dig a tunnel beneath it.
They have opted for a floating tunnel that will be suspended about 100ft under the surface of the water.
This will be deep enough for ships to pass over the tunnel, and will also allow room for passing submarines below.
The goal of the tunnel is to halve the driving time on one of Norway’s main roads, the E39, which runs for nearly 700 miles from Trondheim in the north to Kristiansand in the south.
At the moment, the road is broken up seven times by fjords, meaning motorists must put their cars on ferries to cross.
“It’s nearly 1,100km from end to end – but the journey takes 21 hours on a good day, because of the seven ferry crossings en route,” said Kjersti Kvalheim Dunham, programme manager for Norway’s Public Roads Administration.
“By 2035 we should have cut that to 11 hours by replacing the ferries with fixed crossings.”
The project is not expected to be completed until 2050.