Tower Bridge - London, England, UK

Tower Bridge - London, England, UK.

In the late 1800's, it was clear another bridge was needed across the Thames River. Because the shipping traffic was important to the London economy, the new bridge could not interfer with the tall ships coming to delivier their goods. Conversely, all of those tall ships would be continually distrupting the surface traffic if a drawbridge was constructed.
Tower Bridge was a compromise to these issues. A drawbridge was designed with towers on either end which were connected by a walkways allowing foot traffic to use stairs and cross above the tall ships.
Today, since the need for tall ships has past, Tower Bridge does not open as frequently, so the upper walkways have been turned into a museum devoted to the history of the bridge, the people of the era, and the engineering feats required to build and operate the bridge. Plus you can get some really great views.
Crossing the bridge at street level is free, but visiting the upper walkways require a fee.