6km wide and 800 floors reaching a total height of 4000m, those numbers describe the X-Seed 4000, the tallest building ever fully envisioned. By fully envisioned I mean that the schematics were drawn out and the building structure fully designed. The only thing the project would have required was money.
Between $330 billion and $1 trillion approximately. It would have been expensive were it not for the fact that it was never designed to be built. It was designed for Tokyo as a publicity stunt for the Taisei Corporation. By all means it was a success.
A truly grand vision. Its mountain like shape was very evocative for the Japanese. Especially because of its height. At 4000m tall it would have been 224m taller than that most beloved of Japanese Mountains, Mount Fuji. Additionally it had the capacity to hold between 500,000 and 1,000,000 people. The main concept and development was the responsibility of Peter Neville, a man tasked with many challenges. The greatest of which was the planet.
Unlike most skyscrapers there would be steep pressure changes between the floors, meaning the Pyramid would have to actively control the internal pressure. Also because of the temperature changes at the higher levels it was designed to monitor and keep in check the internal environment with power drawn from Solar panels which were to be strapped on to the external surface.
Furthermore it was built to withstand Tsunamis and the ever possible threat of earthquakes. This design, the size of a mountain will never be built and it may be a long time before someone else fully envisions a construction any larger. However we are fortunate to have decided to design this. It stands as a testament to possibility. It will never built, but if we attempted we definitely could do it.