Free time suggestions in Paris

It depends on your interests- I went to the Pompidou twice and to the Picasso Museum- I also went to the Les Halles neighborhood on my own...Some on our trip went on a tour of the Opera House, one went to Versailles, the Galleries de Layfaette was a destination , some went to other museums on their own, there is SO much to do and see in Paris.. and I know that on day 2 I was 100% comfortable taking the metro and going off alone ( with help from our leader with directions and a map).

The Louvre, Notre Dame, L'Orangerie with Monet's Water Lillies. Best of all may be sitting at a sidewalk café sipping wine and watching Parisian life go by.

An absolute "DO NOT MISS" is Saint Chapelle's stained glass jewel box interior. The church is difficult to see
from the street, because it sits among several official government buildings. It's on Île de la Cité, not far from
Notre Dame. You'll thank me later.

Yeah, gotta agree with medidimmerling. Sitting in a Parisian cafe (on sidewalk, of course) is one of the great
pleasures of life. I will add sipping espresso to sipping wine, and I would add one more attraction to those
whose historic interests bend toward the medieval: The Museé Cluny on Boulevard Saint Michel, just south
of Saint Germain.

I like to use Global Greeter Network greeters.paris/. It's a fun way to have a local show you their city. I have used them in the United States and love them. It's free and you are with a guide on a one to one basis. You sign up well before a trip, tell them what your interests are and they match you to a greeter. You really have to go to the site and see how it works. I highly recommend as no one can show you a city like a local passionate about their city.

I'll be (back) in Paris for a few days before my RS program in Lyon and I am currently thinking about how I will spend my time. Others have already listed many of the main places to see. On my last trip I decided I needed to get off the main thoroughfares that I took from one place to the next, so I started exploring the side streets. The prize was the discovery of a wonderful new museum devoted to language that was not even in any guidebooks. And, of course, sitting in a café (try to find one that is not jam packed) and people watching. Or buying a sandwich and sitting in a park like Place des Vosges or Luxembourg Gardens. Can't wait!
PS I was set up with a Global Greeters guide my last time there. Wonderful experience!

We are going to take the RER C train out to Auvers-sur-Oise where Van Gogh lived, painted and died. It is a short trip out of town and a nice contrast to the intense urban pleasures of Paris. Highly recommend in Paris: shopping in the rue Mouffetard (5th), see Chinatown and the nearby huge murals (13th), the Museum of Jewish Art and History in the Marais is exquisite.

Speaking of train rides, I highly recommend the trip to Chartre to see the Cathedral and soak in the medieval ambience
that still exists there. Anyone whose ever sat through an Art History course will remember Chartres Cathedral.

I would totally second the recommendation about visiting Sainte-Chappelle. It is the most memorable experience for me from my trips to Paris. Don't look up photos about the place; let the experience of seeing those windows for the first time awe you. I would also recommend taking a stroll along the Seine. If you have only one free afternoon, do these two things and don't waste your time traveling out of the city.

Yes, being inside Sainte Chappelle is like being inside a jewel box. I only wish I had been able to attend one of the
concerts of medieval and early Renaisance music which are periodically performed within Ste. Chappelle.