The Musée Carnavalet is the (admission-free) Museum of the History of Paris

Isn't it grand when one of the free sights in town is the museum dedicated to the city itself?

What better excuse to take the time and get under the skin of Paris, from its foundation on Île de la Cité as Celtic Parisii tribe settlement called Lutetia (you'll still see the Francophone version of the name, Lutèce, used around town) and its expansion during the Roman era through the Middle Ages to the epoch where France really started to shine, the Renaissance through La Revolution itself in 1789 (check out the scale model of the Bastille, pre-storming).

What's more, the collections are housed in two neighboring Marais mansions, each a perfect example of Parisian architecture from its two greatest periods: the Renaissance Hôtel Carnavalet (built in 1548 and re-imagined by François Mansart, of roof fame, in the 1600s) and the 17th-century Hôtel Le Peletier—this one with interiors gorgeously re-fitted in the early 20th century.