The O2 Arena from Greenwich Park, London, 2009.

The O2 Arena from Greenwich Park, London, 2009. Designed by Richard Rogers, the Millennium Dome was built to house an exhibition commemorating the arrival of the third millennium. The largest single-roofed structure in the world, the Dome is 365 metres in diameter. The project attracted controversy regarding its cost, the nature of the exhibits it contained for the year it was open as well as the difficulties and expense of disposing of the building after its closure. In 2005 it was announced that the Dome was to become a venue for music concerts and sports events under a scheme sponsored by the telecommunications company O2. It reopened in this form in 2007. (Photo by Peter Thompson/Heritage Images/Getty Images)