Aside from the obvious touristic landmarks/destinations, what else would you recommend to visit in Paris, France?

Notre Dame, Versailles, Louvre, Sacre Couer, Pere Lachaise; been there, or will go there.
But do you know of a sight that we should see?
A nice little, local restaurant?
Cheap book stores?
Anything else, that you’d rather kept secret, but are willing to share with me?
Thanks in advance!