Hammersmith Flyover
The Hammersmith flyover is an elevated roadway in West London which carries the A4 arterial road over and to one side of the central Hammersmith gyratory system, and it links together the Cromwell Road extension with the start of the Great West Road. It is one of the first examples of an elevated road using reinforced concrete.

The Hammersmith flyover is an elevated roadway in West London which carries the A4 arterial road over and to one side of the central Hammersmith gyratory system, and it links together the Cromwell Road extension with the start of the Great West Road. It is one of the first examples of an elevated road using reinforced concrete.
Check the official site before travelling; hours and prices can change.
More bridges

Tower Bridge
The bridge people mean when they say London Bridge. Walk the high-level walkway for the glass floor.

Millennium Bridge
Foot-only suspension bridge from St Paul's to Tate Modern — the only crossing aligned on St Paul's dome.

Hammersmith Bridge
Currently pedestrian-only, Victorian wrought-iron beauty — best photographed at golden hour.
Source: wiki-list