Is there something that can't be done on a Sunday, or for that matter, is there something special on Sundays?
Merci, Ben

You could try the markets in rue Mouffetard, where on Sundays there are various street singers that start around 11am

If you're there during nice weather and you'd like a day off from museums and monuments, you can do what many Parisians do, and picnic at one of the parks where you can actually sit on the grass. Great people-watching. You can read of my recent Sunday in Paris here.

yes indeed sundays is a day of rest in france so many places close or if open at only at half staff;
picnic in the parks is great too; tuileries, parc monceau, luxembourg; boulogne :vincennes all are great parks
having said that: there is always something going on in Paris is non stop you know so if you can give me a date i can tell you whats on.

Jardins du Luxembourg! We were recently there on a Sunday and it was packed with Parisians! It is grand. Take time to have a petit café in the café and watch all of the people watchers!

The flea markets are also open on Sundays - totally different than a slow day in the park.

Street market on Blkvd Richard Lenoir at Bastille: nice enough, but nothing out of the ordinary as street markets go.

There are usually buskers at the place des Vosges in the summer months, and I like a stroll around there and through the Marais, or up the Canal St Martin.