I am on a conference in Paris and I have free time after 7 pm. What can I see at this time? Last time I went up the Eiffel tower, this was great at night and still open. What else can I do?
Which sights have long opening hours?
I’d suggest taking a look at the website of the Paris Convention and Visitors Bureau, which has a page titled “Places to visit at night in Paris”. It lists a number of places (mostly museums, some galleries) that have late openings. The page is unfortunately organized by place rather than by what your options are on a particular day of the week, but the “fact sheet” for every place does clearly list “late opening” on the “prices and times” section.
Here are a few suggestions taken from that page, but organized by day of the week (non-exhaustive list):
Monday: Musée Jacquemart-André (until 9pm, only during temporary exhibitions).
Tuesday: Jeu de Paume Paris (until 9pm).
Wednesday: Musée du Louvre (until 9.45pm).
Thursday: Musée des Arts et Métiers (until 9.30pm), Musée d'Orsay (until 9.45pm), Musée du Quai Branly (until 9pm).
Friday: Musée du Louvre (until 9.45pm), Musée du Quai Branly (until 9pm).
Saturday: Musée du Quai Branly (until 9pm), Musée Jacquemart-André (9pm, only during temporary exhibitions).
There’s also the Palais de Tokyo which is open every day, except Tuesday, until midnight; and the Musée de l'Érotisme is open every day until 2am.
Obviously these times can change, so do check the original “fact sheet”. For most places it also lists until what time before closing time the ticket offices stay open, which would be useful to know.
(Thanks for reopening this question; the above is a slightly extended version of the answer I proposed on the meta SE).
Fortunately ParisInfo (the official tourism website of Paris) has a great few pieces on this:
Places to visit at night in Paris - many museums, theatres and more are open late, including Espace Dali, Musee d'Orsay and the Louvre.
Some places are open very late or all night - but this is more in terms of food, services and shopping.
And finally their piece on night transportation in Paris - covering the Noctillen buses, Metro, RER, taxis and more.