Paris’ second district (arrondissement) is full of so called passages: shopping streets with a roof. A friend of mine made me discover Passage du Grand Cerf and it is my favorite of the many beautiful passages I have seen so far.
Le Passage du Grand Cerf is particularly impressive because of its architecture: a ceiling of glass and cast-iron illuminates the indoor street. And with its 12 meter height it is actually the highest of its kind in Paris. Apparently the passage had been abandoned for a century, but nowadays no such thing can be said about this passage and literally all of the shops are worth a look.
Other than that you will find antique shops that sell oil lamps, letters cut out in wood and other interesting objects. Also, there are several design shops that are a bit more pricey but definitely worth a look for inspirational purposes. To nicely end a visit you can have a coffee in a café at the rue Saint Denis exit. It’s called Le Pas Sage, which is a word game, something that the French love.