Saudi Arabia is planning to build a 75-mile long desert skyscraper worth up to $1 trillion (£833billion).
The Mirror Line, which will have mirrored sides, will cut through mountains and desert and span all the way to the coast and into the water.
It will house five million people and feature a high-speed train running under buildings, vertical farming, a sports stadium and a yacht marina, according to the Wall Street Journal.
The spectacular building will become the epicentre of a futuristic megacity called the Neom.
Neom – which is going to be the size of Massachusetts and located on the Red Sea – has been in development for several years.
The project is the creation of Crown Prince Mohammed bin Salman who reportedly wants to create an architectural marvel as iconic and timeless as the Pyramids of Egypt.
The Prince wants to project to be completed by 2030 – but engineers fear it is so ambitious in scope that it might take 50 years to build.
The Saudi royal unveiled the concept for the Mirror Line last year, announcing that his project would be "a civilisational revolution that puts humans first".
The 105-mile "straight-line city" will be carbon zero, he announced, with no cars and no pollution.
