Also known as the Museum of the History of Paris is in the 4th, on rue de Sevigne, right in the heart of the Marais. Plenty of room recreations, paintings, revolutionary memorabilia, stones from the Bastille, Proust's bedroom and a lovely parterre. My favourite on this visit was the Fouquet Bijouterie designed by Mucha - Art Nouveau at its highest. most sinuous and most gorgeous. Free entry means I will be back time and again as it's literally five minutes from my apartment. Lovely.