The Elizabeth Tower. Commonly known as Big Ben, has seen the history of the city of London, the UK. The tower was set up in 1858. The clock weighs 13. 5 tons. It's the biggest clock in Britain. The sound of Big Ben is part of London people's lives. For over a hundred years, people have listened to its sound. They think of it as an old friend.

The Sydney Opera House is the symbol of Sydney and Australia. Its sail shape attracts visitors around the world. But few people know it has an interesting story. Its designer Utzon got the idea by peeling an orange. It took 14 years to build it, and was finished in 1973.

When you see this pencil-shaped building, you'll know you are in New York. The Empire State Building has 102 floors, which is about 443 meters tall. It took only410 days to build it, and was completed in 1931. The building shows the ambition of humans to build a tower that could reach for the sky.

The Eiffel Tower in Paris stands for French people's creativity and imagination. It was built in 1889. At that time, the tower was thought to be a monster, because it was quite different from the traditional buildings with dome tops. But later it turned out to be a miracle of metal architecture. Now it becomes one of the Europe's most famous tourist attractions.