PARIS, FRANCE

"The City of Lights" is indeed beautiful in every aspect. When it comes to Paris, you need to be prepared. If your dream is to go up the "Eiffel Tower" or to go inside the "Louvre", you need to purchase tickets long in advance, even before you fly to France (if you can't find tickets online, be there around 6am). The lines are the worst I've seen so far. Arrive very early or reserve a whole day just for that.
In case you can't get tickets to go inside the "Louvre", your day is not over. You can walk around its gardens, browse though the statues and admire that gorgeous pyramid.

Tour Eiffel 

Musée du Louvre

After you leave the museum, you can walk down "Voie Georges Pompidou" along "La Seine" river all the way to "Rue d'Arcole" and turning right you will walk about 10 minutes and you will face the MAGNIFICENT "Notre Dame Cathedral", which is a must see.
After that, you should keep walking right on the same street (Rue d'Arcole) and not long after you cross the river, the street name will change to "Rue Dante", keep walking straight for a few minuets until you reach an intersection. At the intersection, you'll stay on "Rue Saint-Jacques", you'll walk about 10 minutes and turn right on "Rue Soufflot" and walk straight towards the beautiful "Luxembourg Palace" and  take a well deserved rest at its stunning garden (Luxembourg Garden).
The tourist sights are not too far from each other, what allows you to choose between walking or taking a cab. I choose walking (SHOCKER!) and I loved every minute of it. I could spend a week walking up and down "Champs-Élysées" and just shopping or choosing where to eat. By the end of that street you will find the "Arch of Triumph" which is also a must see in Paris.

Champs-Élysées

If you have time, visit all these places both day and night, the sights are AMAZING! Paris is indeed one of the most beautiful cities I've ever been to and, despite the horrible cigarette smell EVERYWHERE, I still want to go back many times...