Visiting a museum is a rather casual, albeit elegant, thing to do and putting together that just-chic-enough appropriate outfit could be more difficult than putting together a more formal one. This is because there is no rule for casual-elegant dressing. Above all you want to stay away from looking like going to a cocktail party. Many fashion experts advise to build an outfit from bottom up and in this case, it's more for the comfort than for the fashion side. Whether big or small, we'll be walking and standing around so I think I would rather keep the shoes flat or low enough.