We're used to seeing proposals for high-tech vertical farms that never seem to translate to real life, but the city of Linköping in Sweden has finally taken these buildings out of the realm of glossy CG models. Plantagon International is building a 17-story vertical greenhouse, slated to open by 2013, that will have a "transportation helix" to transfer vegetables and grains within its enormous spherical space. The greenhouse promises to parasitize on the excess heat, CO2 and waste produced by the city, using it for warmth and fertilizer. The design cuts transportation costs, and perhaps most impressively, promises the equivalent of 100,000 square meters of arable land on a 10,000 square meter footprint. Still no word on whether building a gigantic steel and glass structure is more carbon-efficient than conventional farming, but retrofitting existing office buildings might help take care of this problem.