Considering the L'Atelier De Montparnasse in Paris?
A VT member wrote the following comment about visiting Paris:
Mondays and Tuesdays by sourbugger
Due to the fact that the major museums operate weekends, it is still customary for the major museums to shut one day within the working week.
Whilst this is an inconvenience, it is of course possible to plan around it.
Places live the Lourve and the Pompidou shut on Tuesdays and the Orsay on Mondays.
Check out the websites of the museums you plan to visit in order to confirm details and plan accordingly.