If you’re lucky enough to reside in Nice or one of the 49 communes of greater Nice (Métropole Nice Côte d’Azur) you are entitled to the pass ‘Pass Musées de Nice” that gives you free access to 14 of the city’s municipal museums and galleries.
To obtain one you need to show:
1) A valid passport or national identity card and
2) Verification of your address (dated less than 3 months)
Take your 2 verifications to the reception at any museum or municipal gallery where you will be issued a pass. The pass is valid for all residents over 18 years of age, and is valid for 3 years. (Children and under 18 years of age are free anyway).
The list of the 49 communes can be found here: http://fr.wikipedia.org/wiki/M%C3%A9tropole_Nice_C%C3%B4te_d’Azur