I have found that the city of Paris' Cité de l'Architecture et du Patrimoine, is rarely on the To Do Lists of my friends visiting Paris. This is one of the most beautiful museums and can easily be added to your itinerary when you are at the Palais de Chaillot at Place du Trocadéro. It also offers commanding views of la Tour Eiffel from the expansive windows overlooking the Seine. The entrance fee is nominal and on free on the first Sunday of the month.
1 Place du Trocadéro