I've lived in Paris for over 2 ½ years now, and I still love to be a tourist from time to time. Those inclinations certainly increase when the prospect of “free’ is involved.
If you’re ever in Paris on the first Sunday of the month, be sure to look into free openings (pop over to Parisinfo.com for a complete listing). That’s just what I did last month on the first Sunday of November - and realized that additional sites participate during the low-season of November-March. It allowed me a free climb up the Arc de Triomphe to see the view at night.
Take advantage of free admission if you are in town this Sunday!