overrated

Located in Paris, France, the Eiffel Tower was built for the International Exhibition of Paris of 1889 commemorating the centenary of the French Revolution. At 300 meters (320.75m including antenna), and 7000 tons, it was the world's tallest building until 1930. The Eiffel Tower was almost torn down in 1909, but was saved because its antenna was used for telegraphy at that time. As other comments have noted, the engineering is not that notable; however, the social and historical significance of the structure is immense.

It's not really a building in the strictest sense - it's a structure. But, it is instantly recognizable, is unique, and is enduring (unless some terrorists get mad at the French for some reason and decide to demolish it).

Architechurally, the Eiffel Tower is nothing big; it's just a tower that was erected in the late-19th century and was supposed to be taken down shortly thereafter. But an interesting thing happened; people got used to seeing it everyday and it became a landmark. Really, it's a mass of steel that evokes no architechural heritage. The views from the top are great though; all of Paris can be seen from there. Going to Paris and seeing it is an incredible experience. Paris would be totally different without it.