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There's a very umbitious project in Japan, a mega pyramid city where you get the most people living and working in the smallest area. It would be the most populated place ever existed.
It's all planned and apparently they really want to do it, they are just dependent of some technological advances.
The structure would be more than 14 times as high as the Great Pyramid of Giza (139 metres, 456.04 feet), and would house 1,000,000 people.
The proposed structure is so large that it could not be built with current conventional materials, due to their weight. The design relies on the future availability of super-strong lightweight materials based on carbon nanotubes presently being researched.
And it seems will be energy independent. Because they would build it near a lake, where they are developing algea and how to get energy from it.