If you go to the Eiffel Tower you should avoid the elevators (where will have to wait at least one hour) and take the stairs. It is far easier that it seems until the second floor (the third being quite high). Morevoer climbing inside the tower make feel being in the heart of the structure and let you take time to see
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You can't visit Paris without seeing the iconic Eiffel Tower! Don't forget to visit at night to see the lights sparkle.
There is a piece of history in almost every corner in Paris, so the best is to walk around and discover the arrondissements and don't forget the museums, especially Marmottan Museum in 16ème arrondissement.