Please note there are restrooms by the Charlemagne statue on the Place du Parvis Nôtre Dame and also in the Jardin du Luxembourg near the Médici fountain (on the east side of the garden). You'll pay a small fee to the attendant for use of the toilette.
Also, there are sanisettes throughout the city. These are self-cleaning and very sanitary. Please be advised that once you open the door to leave, the sanisette will start to clean itself so you'll need to move quickly or otherwise risk being sprayed with a ton of water! SANISETTES ARE NOW FREE IN PARIS! Please see website below for locations throughout the city.
I saw them at:
149 Bd St-Germain (near St-Germain)
Place de la Bourse
Rue de Belleville
The other alternative is to go into a nearby bar (there's always one somewhere on the block!). Use the facilities (usually downstairs in le cave), buy a drink then move on.
One time I tried using the outdoor facilities that were by Sacré-C?ur but the doors on every one of them were jammed from vandalism. Oy vey!But the best places to use les toilettes are inside the Ritzy (pun intended) hotels as they are super nice. The one in the Ritz has wooden tray on the table with perfume and other toiletries items a woman might need.
We have a joke in our household where we call toilet paper, papier de toilette. I noticed the sign on the inside of a sanisette that calls it Papier Hygiénique so (you know me) I had to take a photo! I guess we'll be calling it that instead from now on. ;)
Photos: Feb 2006 & Nov 2007

