The Gherkin is a commercial skyscraper in London's primary financial district, the City of London. With 41 stories it is 180 metres tall and stands on the former sites of the Baltic Exchange and Chamber of Shipping, which were extensively damaged in 1992 by the explosion of a bomb placed by the Provisional IRA in St Mary Axe, the street from which the tower takes its name. After plans to build the 92-storey Millennium Tower were dropped, 30 St Mary Axe was designed by Norman Foster and Arup Group and it was erected by Skanska, with construction commencing in 2001. The building has become a recognizable feature of London.
The building uses energy-saving methods, which allow it to use half the power that a similar tower would typically consume. Gaps in each floor create six shafts that serve as a natural ventilation system for the entire building. Architects promote double glazing in residential houses, which avoids the inefficient convection of heat across the relatively narrow gap between the panes, but the tower exploits this effect. The shafts pull warm air out of the building during the summer and warm the building in the winter using passive solar heating. The shafts also allow sunlight to pass through the building, making the work environment more pleasing, and keeping the lighting costs down.
On the building's top level (the 40th floor), there is a bar for tenants and their guests, featuring a panoramic view of London. A restaurant operates on the 39th floor, and private dining rooms on the 38th. Whereas most buildings have extensive lift equipment on the roof of the building, this was not possible for the Gherkin, since a bar had been planned for the 40th floor. The architects dealt with this by having the main lift only reach the 34th floor, and then having a push-from-below lift to the 39th floor. There is a marble stairwell and a disabled persons' lift, which leads the visitor up to the bar in the dome.