When the Eiffel Tower was first built, lots of people in Paris hated it. They thought it looked like a giant ugly piece of scaffolding stuck in the middle of their beautiful city. It was only meant to stand for 20 years and then be taken down again.
It was saved because it turned out to be brilliant for sending radio signals - the tower's height made it perfect as a giant antenna. By the time the 20 years were up, no one wanted to take it down any more. Today, around 7 million people visit it every year.
The tower is made of 18,000 pieces of iron held together by 2.5 million rivets - little metal bolts. It was put together in just two years by 300 workers, which was very fast for such a big building back then. The whole thing weighs around 10,100 tonnes.
On a hot day, the tower actually grows. The iron expands in the heat, so the top can lean as much as 18 centimetres over to one side - about the length of a pencil. When it cools down at night, it shrinks back. The tower is also repainted every seven years, by hand, with around 60 tonnes of paint.