Anything to see or do in Paris during the night?

When will you have your layover in Paris? There are plenty of activities to do at night in Paris.

https://worldinparis.com/paris-nightlife-fun-things-to-do-in-paris-at-night

It would help to know your arrival and departure times (CDG, I assume?), as well as time of year. The RER to and from CDG is not 24 hrs. You need to allow for passport control on arrival plus exit formalities before departure as well as transit times coming and going - all of which could add up to 5 hours minimum.

I've never felt unsafe walking along the main boulevards at night, but I don't think that would be very comfortable during the colder months.

When you say middle of the night, do you mean overnight? Midnight to 3 or 4 am? I’m very comfortable walking alone in Paris at night, but would not want to be out after 1 am or so in some areas. Please let us know more details.

Thank you all so much for your willingness to help me! My layover in Paris (CDG) is August 10th at 7:35 pm to August 11th at 10:15 am.

The city's bridges and beautiful buildings are illuminated until midnight, cafes and bars will be open at least till then in some places. You'll probably want to take a taxi back to the airport (it's a fixed rate, don't know what it is). Where are you going to sleep? Maybe get a bed in a hostel for a few hours? Some sights are open late. I think the Arc de Triomphe is open until 11. There are late evening Seine cruises - check the website for Les Vedettes du Pont Neuf.

In August it is still light quite late.

A taxi to the Left Bank (Eiffel Tower) will be a fixed rate of 58€; to the Right Bank (Arc de Triomphe), it will be 53€. The same from either of those locations back out to the airport.

I normally count on it taking an hour from the time the plane lands until I am out the front door of the airport; and another hour to get into town (on any given day this may be shorter or longer, of course).

Allow for an hour to get back to the airport, and if your departure the next day is for a trans-Atlantic flight, you will need to be back at the airport three hours before departure.

I took a visiting friend on an evening walk last August. We started at 8pm. Her obsession was to see Eiffel Tower sparkle, but it was not lit until 10pm (sparkle for 5 min on the hour). We popped into a supermarket to pick up picnic food first. Since Paris Plage (Paris Beach) is in full swing in August, we walked from Pont de Sully (under the bridge, on the Right Bank, aka Marais side) along the river bank full of people/ cafe /musical performances, all the way to Pont des Artes. Go up to street level here, into le Louvre, to Pyramid (already lit) where we had our picnic, into Jardin de Tuileries, walk all the way across to see Place de la Concorde, back track half way to go across Pont de Solferino to the Musee d'Orsay side, down to the water front and walk pass lots of people/cafe/bars all the way to Pont Alexandre III. Go up to the street level to look at Les Invalides (lit)/Petit Palais /Grand Palais. My friend wants the long shot photo of Eiffel Tower, so we took metro to Trocadero and watched Eiffel Tower sparkle (huge crowd!). We walked down towards Eiffel Tower to the street level for a close-up look. That area was full of people. 2 options to get out of there: bus 72 (at Pont Ilena) which runs along the river all the way to Gare de Lyon, or walk all the way to metro Ecole Militaire (vicinity rue Cler area with many cafe/bar/restaurants open late into the night). We ended at midnight. It was very safe, but high pickpocket risk b/c huge crowd. Note that Paris metro stop running at around 12:30am. There are night buses during the no-metro hours.

Thank you all so much for your wonderful suggestions!