Recs for sites in Paris away from the crowds?

Don’t miss l’Orangerie which has many of Monet’s water lily paintings.
I would reconsider staying in the 7th. Either the 5th or 6th would be less touristed.

I love the 7th and find that where I stay it's not particularly crowded.

When I was in Paris in October I found the Orsay, Louvre and Orangerie were terribly crowded. In fact, due to crowding in the Orangerie I skipped the Waterlilies on the entrance level and headed downstairs where it was literally shoulder to shoulder in what previously would have been fairly empty rooms.

I did find the Cluny fairly empty but the day I went about half of it was closed. I think it was due to staffing issues but they were not real clear on that. The room with the Lady and the Unicorn tapestries was open which is always my target there. I actually had the room to myself a few times out of maybe 15 minutes. I could easily sit on the bench area and look my fill without feeling like I needed to move on.

I also went to Basilica Saint-Denis on the north end of town. It's an outstanding example of Gothic architecture. I'd been there a number of times and it is never crowded and this day proved no exception. I got myself tangled up on museum closures and wound up on a Monday without a plan in place and all my museum choices booked, so headed up there. It was perfect. There were a few school groups there ranging from what looked like university aged students to little ones holding hands but it did not feel crowded even in the crypt.

I finally made it to the Museum of Hunting and Nature which has been on my "to-do" list for years. It was surprisingly crowded. There was a new exhibition opening and it was school break so lots of families were visiting as well as folks who were clearly there just to see the exhibition. I thought this museum was interesting and perhaps it will not be as crowded next time I drop by.

The Louvre is always crowded along the trail to the Italian paintings section and the Mona Lisa but if that is not on your list of things to see then there are areas where it is relatively uncrowded. You have to be determined to get thru the scrum under the pyramide but I always stop by to see the Vase of Alienor d'Aquitaine in the Richelieu wing as well as the rooms with the Vermeers and Rembrandts one floor up. Also on the top floor of the Sully wing are, perhaps surprisingly, a room of Impressionist paintings including a few by Monet and Degas. Here is a link to gallery closures so you can decide what you want to see on your visit.

https://www.louvre.fr/en/visit/list-of-available-galleries

Although I did not go this last trip, my prior trip in 2023 I did the Quai Branley Museum which was deserted. Haven't been to the Guimet in a number of years so not sure if it's picked up crowds or not. I also enjoy the Museum of the Resistance and Liberation which is across the street from the entry to the Catacombs and is free but did not go this last time. Army Museum is usually relatively uncrowded and it may be very convenient to where you are staying in the 7th but it depends on if you are interested in military history or not.

I visited the Petit Palais in October as well. It's a free City of Paris museum, charging only for their special exhibitions which are wonderful. I was shocked at the crowds at this museum as well. Every other time I've been there it's been pretty sparsely visited but wowser. The special exhibition was jammed (Swedish artist) as well as many visiting the free galleries.

Have a wonderful time!

I'd suggest Petit Palais and the cool "architecture" museum...but it's much more than that.

Two sights that may be less busy that I have not yet had the chance to visit are Marmotten (Monet paintings) and the Carnavalet. We enjoyed our time in Chartres. The city is quite attractive and of course the cathedral is jaw dropping. (I strongly agree with the comment below, nighttime in Chartres is quite enjoyable. It wouldn't be my first choice, but if staying overnight in Chartres is not possible, I see no reason why you couldn't stay into the evening and head back at 9ish.)

https://www.marmottan.fr/en/

https://www.carnavalet.paris.fr/en

Maybe this might be of interest to you in Paris while escaping the crowds: The French Naval Museum located in the Trocadero, assuming you're interest in military history.

The US and France share a common history here as the 2 countries found themselves once engaged in a so-called "undeclared" Naval War.

A few things we have enjoyed in Paris that are a bit off the beaten path:

-Musee des Arts Decoratif (this is next to Louvre and has stunning but manageable collection shown in chronological order, also a beautiful gift shop) https://madparis.fr/musee-des-arts-decoratifs

-Le Corbusier Foundation https://www.fondationlecorbusier.fr/en/tickets/

-Musee de Musique (the audio guide lets you hear dozens of historical musical instruments being played, there are also concerts) https://philharmoniedeparis.fr/en/musee-de-la-musique

-Musee Quai Branley (practically under the Eiffel Tower, beautiful displays and great audio guide with collections from the areas former French colonies) https://www.quaibranly.fr/en/missions-and-operations/the-musee-du-quai-branly

Enjoy the planning!

If you do Chartres, do it as an overnight so you can see the illuminations. Usually the last train to Paris is too early to stay and watch the show and it is really worth it. We did an overnight last spring and really loved it.

We really enjoyed visiting the Marmottan museum which is devoted to works by Monet. It is a museum many people haven't heard of but still has an impressive collection. You can find videos online filmed there to decide if the museum is a place you'd like to visit.

KOB,
As others have said throughout the forum, for the Orsay museum, get an early reservation and go to the top floor right away for the best example of Impressionist paintings without the crowds, then work your way down to the lower floors. The Rodin museum, I find, is best appreciated in the garden, with its wonderful sculptures. If you don't make it inside his house, you will still have had a wonderful experience. Be sure to take note of "The Burghers of Calais" and the doors "The Gates of Hell". And the gardens are lovely as well, with places to sit and relax. The Invalides (army museum) is usually not crowded, is large, and has a wonderful collection of suits of armor. Napoleon's tomb may be crowded or it may not be, but is still worth seeing. The Eiffel Tower, Champs de Mar, Invalides and Rodin Museum are near to each other, and make a nice loop for a day. We usually go from the ET, then the Invalides, lunch at the cafe at the Rodin, a stroll through the sculpture gardens there, then a walk to the beautiful Pont Alexandre III. From there, depending on the time, you may want to get a boat ride on the Seine or walk across it to the Petit Palais, which I hear isn't usually crowded.

KOB,
Do try to see the Cluny Museum. We were there at the very end of May in 2023 and walked right up and didn't encounter any crowds. It was a weekday, and schools were in session. We did encounter one small school group but never felt hemmed in. It is a fantastic museum of medieval arts in a great setting!

I can recommend the Musee Carnavelet - I was frequently the only person in a room there and I particularly like the basement with the ancient artifacts. For the same reason I like the archeological crypt in front of Notre Dame. Have never seen it crowded and there is a real feeling for the history of Paris before what you see now.

The Picasso Museum had people, but it was relatively uncrowded and pleasant to enjoy. There were very few people in the Victor Hugo home. I have never been crowded in the gardens of the Musee Rodin and it's a particular favorite, and though inside may be a bit crowded, it's not off-putting.

For the Musee d'Orsay, consider taking the first time in the morning. It takes an hour or so for the crowds to get intense. I haven't found the Louvre unbearable once inside except in the vicinity of the Mona Lisa, but I haven't been in a few years.

On the day I went last January the Musee Marmottan was shoulder to shoulder and because part of it is essentially in a mansion, the traffic doesn't flow that well through the rooms. Perhaps on a weekday it would be less crowded.

Practically no one was in Marie Curie's laboratory and the Pantheon wasn't crowded once you are inside even though there was a line to get in. Definitely get that ticket online if you want to go in.

Something else I did where there were really no crowds was to go into every church I passed. I was frequently nearly alone, more than once I heard an organ practice. If you are into music, you might enjoy an evening concert in a church. I attended one at St. Germain des Pres and it wasn't crowded at all and the price was reasonable.

Great suggestions above. See also this link for some more ideas:
https://community.ricksteves.com/travel-forum/france/paris-sightseeing-3e19f0e6-356c-4a7f-b574-500fdb431010

I've had 3 visits to Paris in the past couple years - what I've noticed is that even those museums that are generally less well known are sometimes full although not my definition of "crowded" on Saturdays and Sundays. Among those that I found "well populated" on a Saturday/Sunday two months ago were the Musée des Arts et Métiers with lots of parents and school age kids (actually quite sweet family outings), the free City of Paris museums - Carnevalet and Maison de Victor Hugo, and the Picasso Museum. None were so crowded that I couldn't enjoy fully.

• Musee Carnavalet (history of Paris; in the Marais, near Place des Vosges),
• Sunday morning at St Sulpice for organ recital before?after? Mass (st Germaine; not far from Luxembourg Gardens),
• Maison Balzac (wonderful woodcuts used in printing his Comedie Humaine novels; lovely views; 16th Arrondisement),
• Passages Couverts (Galerie Vivienne, Passage Jouffroy, Passage Verdeau to name a few of the 25 or so passages; 9th, 2d, 4th and other Arrondisements walking tour),
• Museums at Luxembourg Gardens or Petit Palais if there are exhibits of interest to you while you are in Paris.

Will you be in Chartres when Chartres en Lumieres is running? Seems likely. If so, consider spending a night there. Dress warm for that.

Just wondering if any one has made it to the Cité de l'économie et de la monnaie
It is #1 to visit on my next trip to Paris. It seems to be a very interactive museum, and the building itself seems worth a visit.

Night hours won't limit the crowds much at the Louvre or the d'Orsay. The best you can do at either is get the first entrance time and go all the way up and work down. The Orangery has those fantastic murals, but the crowd ruins the who thing.

If you have any interest in aviation I highly recommend the Musée de l'Air et de l'Espace; it's fantastic and the only crowds will be school children.

If you're into art and want something to remind you of the trip, provided the timing is right, visit https://www.fleamapket.com/listing/foire-aux-puces-de-crevecoeur-le-grand/

I can recommend Musée de l'Air et l'Espace too. No crowds at all there and I was so lucky visiting it during the professional days of the airshow, so the days before the general public. Meaning enjoying the demonstrations of several airplanes actually for free as there was no extra charge on top of the usual museums admission fee.