London, England: Tower Bridge

London had a problem in the late 19th century. It needed another bridge across the Thames. The catch was, the city couldn't build a typical bridge because that would mess up shipping to the port areas.

The Tower Bridge was the solution. It has the elements of a drawbridge, so that large ships could pass through safely.

A total of 40,000 people still cross it every day, in one form or another, with a speed limit of 20 mph for vehicles. Some stop at an exhibition for a quick lesson in the structure's history. And the bridge is still raised about 1,000 times a year to allow ships to pass through. At least 24 hours notice is required.

You can stop in the middle and take the tour of the area. It should be noticed that the lines can be long for this activity during tourist seasons. However, it's great fun just to walk across it and enjoy the views. Indeed, it's tough not to take a ton of photos of the bridge and from the bridge during a visit.