Millennium Dome (London, U.K.)
Once regarded as a political embarrassment and economic disaster, the Millennium Dome (later rechristened the O2) has since bounced back as a concert and sports venue. Puffing up from East London's dodgy Docklands area like an enormous, glowing sea urchin, it encompasses a sprawling and virtually uninterrupted internal space using remarkably little material: roughly 1-2 pounds per square foot (4.9-9.8 kilograms per square meter), compared to the 30-40 pounds (146.5-195.3 kilograms) typical of most roofs [sources: Gross; Lyall; RSH+P; Solomon].
The mutant urchin's spines are actually 12 steel masts (one for each month), each towering 328 feet (100 meters) and together supporting a Teflon-coated, glass-fiber roof above more than 1,076,000 square feet (100,000 square meters) of enclosure. The building measures roughly 1,200 feet (a symbolic 365 meters, one for each day of the year) across and 0.62 miles (a full kilometer) around, and reaches a maximum height of 164 feet (50 meters) [source: RSH+P].
Whether the dome represents an environmental triumph or tragedy remains controversial. Its construction drove a massive toxic waste cleanup and area reclamation project, and used remarkably few materials. Unfortunately, its polytetrafluoroethylene roofing material (PTFE, better known as Teflon) generates ozone-harming chlorofluorocarbons (CFCs) and hydrogenated CFCs when produced. Still, it beats the original plan to use dioxin-linked PVC-coated polyester [sources: Higgs; Melchett; Williams].