City Hall is the headquarters of the Greater London Authority (GLA) which comprises the Mayor of London and the London Assembly. It is located in Southwark, on the south bank of the River Thames near Tower Bridge.
The building has an unusual, bulbous shape, purportedly intended to reduce its surface area and thus improve energy efficiency, although energy use measurements have shown this building to be fairly inefficient in terms of energy use, with a 2012 Display Energy Perforance Certificate rating of “D”. It has been compared variously to Darth Vader’s helmet, a misshapen egg, a woodlouse and a motorcycle helmet. Former mayor Ken Livingstone referred to it as a “glass testicle”, while the present mayor, Boris Johnson, has referred to it as “The Glass Gonad” and more politely as “The Onion”. Its designers reportedly saw the building as a giant sphere hanging over the Thames, but opted for a more conventionally rooted building instead. It has no front or back in conventional terms but derives its shape from a modified sphere.
A 500-metre (1,640 ft) helical walkway, reminiscent of that in New York‘s Solomon R. Guggenheim Museum, ascends the full height of the building. At the top of the ten-story building is an exhibition and meeting space called “London’s Living Room”, with an open viewing deck which is occasionally open to the public. The walkway provides views of the interior of the building, and is intended to symbolise transparency; a similar device was used by Foster in his design for the rebuilt Reichstag (parliament) in Germany. In 2006 it was announced that solar photovoltaic cells would be fitted to the building by the London Climate Change Agency.