Ever wondered how tall the tallest building ever designed is ? There’s a lot of debate about what the tallest tower in the world currently is. Some say the Taipei 101 is the world’s tallest tower, whereas we might argue that the Sears Tower, still takes the prize. Forget about the Taipei 101 Tower, or the Sears Tower. If the enormous, 13,000 ft X-Seed 4000 structure ever gets built in Tokyo – it will win the worlds-tallest-building competition. We use the word “building” loosely, because this is seven times taller than the current tallest building, and actually 700 feet higher than the actual Mt. Fuji. The X-Seed 4000 proposed 4000 meters (13,123 foot) height, 6 kilometers wide sea-base, and 800 floor capacity could accommodate five hundred thousand to one million inhabitants. The mountain-like X-Seed 4000 represents a utopian eco-vision for a self-contained high-rise city of about 4000 meters high in Tokyo, Japan! Designed by Taisei Construction Corporation, as an “intelligent building” the super-futuristically-named X-Seed 4000 would maintain light, temperature, and air pressure in response to changing external weather conditions. Solar Energy would power the X-Seed 4000 which could house between 500 000 to 1 million people. The projected cost of a building like this have been estimated between $300 to $900 billion. We’re not saying it’s impossible, but for now, X-Seed 4000 seems like more of a utopian vision for contemporary green urban planning than a viable design solution.