Sky City 1000 is a concept for an artificial city rising 1000 meters above the ground and covering an area of 800 hectares (2000 acres). Incorporating functions for a medium-sized city (housing, retailing, education, recreation), this 21st century vertical community would be a synergistic fusion of transportation, communications and energy aimed at helping put an end to major congestion and lack of green space in the Tokyo, Japan ward area.
The plan consists of a building 1,000 meters (3,280.8 feet) tall and 400 meters (1,312 feet) wide at the base, and a total floor area of 8 km² (3.1 mi² or 1976.8 acres). The design, proposed in 1989 by Takenaka Corporation, provides for 35,000 full-time residents and 100,000 workers. It comprises 14 concave dish-shaped "Space Plateaus" stacked one upon the other. The building would include residences, offices, commercial facilities, schools, theaters and other modern amenities.
Since its announcement it has garnered much attention among the world's architectural establishment. Many hope that within a decade or so it will be fully realized by the Tokyo Metropolitan Government and Japan's largest corporations. Apparently, the project is taken very seriously and Tokyo's only fire helicopter has been used in simulation tests to see what the danger would be if a fire were to break out in one of the buildings. Also, triple decker high speed elevators which would be used in the building and would contain up to 70 people are being designed in experimental labs outside Tokyo.
Although this project has gained more serious attention than many of its alternatives, it can be considered similar to projects such as X-Seed 4000 and Sir Norman Foster's Millennium Tower and, in ultra-high density, mixed use concept, to theories like Paolo Soleri's Arcology and Le Corbusier's Radiant City.
(Information comes courtesy of the Wikipedia amongst other sources.)