First important point: If you want to travel around Paris, this thing is very useful. If you stay on the outskirts of the city, it's absolutely essential!
Second important point: Forget Eiffel Tower. More precisely: Visit Eiffel Tower but don't climb it as every other pathetic loser. If you don't pay for the mega-expensive restaurant at the top, you can only climb as high as the second "level", approximately in the middle of the tower (i.e. not very high), and feel like a prisoner behind the steel mesh, amongst hundreds of screaming tourists. Instead, go to Montparnasse 56 Tower which is almost exactly the same height as the Eiffel Tower and you can either take lift to 56th floor where you find observation deck, souvenirs and two restaurants, or take short stairs from 56th floor to the roof and see whole Paris, including the Eiffel Tower. It's breathtaking and it's far less crowded:
This video is taken shortly after the photo above. Stormy night after the dark 200 meters above Paris is amazing experience (although the video is rather shitty):
Third important point: The Louvre is vastly overrated. All the accompanying texts are only in French. Mona Lisa is small and probably a replica (bored guards did nothing when hundreds of visitors photographed her using flashes from 2 meters away, which was supposed to be "strictly forbidden", according to the nearby signs). The three most important paintings in The Louvre are:
- St. Franciscus of Assisi (i.e. me!) and paragliding Jesus in laser beam shoot-out.
- A zombie (???) with saw in his head.
- An early portrait of Jigsaw from the "Saw" movies.
UPDATE: It seems I am completely wrong about the Eiffel Tower and you can take a lift to the very top for 12 Euro...? Whatever. It's many years since I was there and Montparnasse Tower was better...