Go inside the Sainte-Chapelle on a sunny day.
Grab a falafel sandwich from one of the stands in the Jewish Quarter, rue des Rosiers, then get lost walking in the Marais.
Take some leftover baguette to the Jardin des Tuilleries and feed it to the enormous carp in the round basins.
Go to the Sunday morning bird market on Île de la Cité on, buy some pigeon food, then go feed the pigeons in the park behind Notre Dame.
Visit Shakespeare and Company, the historic little English bookstore on the left bank quai across the river from Notre Dame.
Then walk a bit down the same quai to one of the oldest churches in Paris, St. Julien-le-Pauvre. On its grounds is the oldest tree in Paris.
Watch the sunset from the steps in front of the Sacré Coeur basilica on Montmartre.
When you’re in the neighborhood of the Louvre, find St. Eustache, a homely hulk of a church on the outside, quite beautiful inside. Tourists never go here because it’s so unpromising looking, but it used to be the church that served les Halles, the old wholesale market of Paris.
While you’re near les Halles, hunt up the 130 year-old shop of the exterminator Julien Aurouze, 8, rue Halles. You’ll see why when you get there.
Get some macarons from Ladurée, croissants (or anything, really) from Dalloyau, chocolates from La Maison du Chocolat, and go smudge the windows at Fauchon.