The XSEED 4000 is currently on the drawing board for construction and if it receives the green light, will be the world's tallest populated structure at a whopping 13,000 feet. Just to put that into perspective, the current reigning champ is Taipei 101 at a mere 1,671 feet.
Not only is it destined to be the tallest but also the largest self-sustaining structure. Designed to look like Mount Doom Mount Fuji, the XSEED 4000 represents the Japanese view of a utopian society. The building will be powered by solar energy and can house up to 1 million inhabitants.