La Rive Gauche is where the artists, writers and philosophers are --the heart of bohemianism & counterculture. Stroll around, soak it in! Say hi to John for me!
Probably my favorite museum in Paris, mostly filled with Impressionist art. Make sure you go to the top and walk behind the clock. It's a really nice shot.
Try some Aligot, a traditional dish from le Sud Ouest made from melted cheese blended into mashed potatoes, and served with a steak or sausage. It's amazing.
The Catacombes de Paris is an underground ossuary which holds the remains of about six million people. Check their website for opening hours. Lines are LONG.