While I hope that you're able to travel to many places in your life, if you only ever went to Paris, you would still have an amazing adventure. Paris is a unique place. I've been lucky enough to visit Paris several times, and I'm in the process of planning another trip.
If you're planning to travel to Paris, I have a few recommendation about places that you should visit while you're there. Of course, there are so many different things to do in Paris, but these are a few of my favorites.
Musée Rodin - Another great art museum in Paris. In addition to the art itself, this museum has a beautiful garden. You will see Rodin's famous The Thinker. There are also plenty of other statues scattered among rosebushes and other flowers. If you are in Paris during the warmer months, you must spend time in the garden.
Palais Garnier (Opera House) - If you have seen The Phantom of the Opera, you may recognize this place. Yes, the book is set in this Opera House. The inside of the Opera House is absolutely stunning.
Sacré Couer - Head up to this Basilique in Montmarte for one of the best views of Paris. On the way up be sure to stop by the artists' stalls and take a look at the paintings. There are also a few good places to stop for crêpes in Montmarte, so I'd advise that as well.
Louvre - You knew that this one would be on the list. Chances are that you do want to see the Mona Lisa. There is lots of art to see in this museum. You could spend days in there, and not see everything. That being said, if you're pressed for time or if you want to avoid crowds and art isn't your thing anyway, you might want to chose a different art museum.
Notre Dame - While you could just view Notre Dame from the outside, it's worth taking the time to walk through the inside as well.
Eiffel Tower - It's up to you to decide whether you want to spend the time and money to go to the top of the Eiffel Tower (I personally would, but it's ok if you don't). However, you should explore the area in front of the tower. Bring a picnic for a meal and enjoy the view. Also, the Eiffel Tower sparkles on the hour at night until midnight. You need to see this.
Other Things to Do
Eat a crêpe. This must be done. I'd advise nutella and banana.
Walk down the Champs-Élysées. This where many famous shops are. You'll want to window shop. Stop by Laduree for a macaroon or two if the line isn't too long.
Spend a day at Versailles. Where Marie Antoinette lived. The palace is stunning. It's outside of Paris, so visiting it will involve a day trip.
Walk along the Seine. Either bank of the river is good for walking and people watching.
Shop at Galleries Lafayette. You don't actually have to buy anything at this huge department store, but you should take a look around. It reminds me of Macy's in New York or Harrod's in London.