Hidden Gem Paris Suggestions?

I was going to suggest the Pasteur Museum, but noted the website says it is closed until November 2028 for renovation. If you have a far off trip planned, remember this museum…….

You are going to get a million suggestions from generous posters!

WWII - The Liberation Museum in its current form is a new option from 10 years ago. Highly recommend.
https://www.museeliberation-leclerc-moulin.paris.fr/en

So many art museums - which have you visited? You are going to be directed to places like Musée Marmottan Monet and Rodin that you may have visited already. If you like porcelain, I can recommend the Sevres Museum which is typically not on travelers' radar. Watch the lunch hour closings, but other than that, easily accessed.

https://www.sevresciteceramique.fr/en.html

Activities - not mentioned, but I enjoyed a perfume making workshop at Fragonard. There are other options as well.

Check this out: https://www.ricksteves.com/europe/france/paris. Scroll down and click on the + sign on the right of At a Glance.

Not hidden, but I go every time in Paris to the Rodin Museum. I never tire of wandering the garden and appreciating his particular gift. The Burghers of Calais is always worth contemplating. And I finally got to the Cluny Museum in 2023! For medieval art in a wonderful structure (that isn't in Italy), you can't beat it. So if you haven't been to either, or the Cluny visit was years ago before its refurbishment, go now.

P.S. Lots of people forget about the Cathedral of St. Denis because of its location. Go! It contains the tombs of many French monarchs and is a beautiful church as well.

Rodin Museum
Canal St Martin
Albert Kahn Museum and Gardens

Butte-aux-Cailles in the 13th is interesting

You emphasized hidden gems. 1 The first is the Paris sewers tour: https://musee-egouts.paris.fr/en/. Most visitors tour the worthwhile Catacombs, but the sewer tour is quite interesting. Most people are grossed out, but I found it fascinating. 2. Visit St. Germain des Pres on Boulevard St. Germain, the oldest existing church in Paris: https://parisjetaime.com/eng/culture/eglise-saint-germain-des-pres-p1011. It was founded in 558, though the oldest part today is from the 12th century, which is still impressive. The church was extensively restored in recent years, and the interior is stunning. When I first visited in 2012, I came across a university group from South Dakota that specialized in liturgical dance. I told them they made me proud to be an America. 3. Place des Vosges is a city within the city and the oldest square in Paris: https://www.parismarais.com/en/discover-the-marais/the-marais-neighborhoods/place-des-vosges.html and https://en.wikipedia.org/wiki/Place_des_Vosges. It's was a fashionable place to live in 17th and 18th century. It houses the Victor Hugo House museum: https://www.maisonsvictorhugo.paris.fr/en

Have you been to the Louvre branch (not far) for Decorative Arts and for Fashion? Have you had lunch/dessert at Angelina? (Rue de Rivoli) (No torn t-shirts, probably.) Official tour of Palais Garnier? Have you been to the church just to the left of the Louvre palace, where the St. Bartholomew's Day massacre started out from? Musée des Arts et Métiers?

The WWII museum that ORDtraveler mentioned is just across the street from the entrance to the catacombs and is really well done. It’s also fairly small, making it a good choice for a late morning or early afternoon (just before or after lunch). Loved it.

I was just in Paris and enjoyed a visit to the Carnavalet Museum which focuses on the history of Paris through some wonderful art, many interesting artifacts, and good signage in several languages telling the story of Paris over the years. It’s located right in the Marais neighborhood and, best of all, it’s free with no lines!

The Pere Lachaise cemetery is a wonderful excursion. I followed Rick Steve’s’ audio tour with success to see some of the most visited and/or interesting gravesites. Enter at the Gambetta entrance to start his tour and, more importantly, to go mostly downhill. This is another free activity.

By the way, if you are planning to visit the restored Notre Dame, don’t bother with trying to get timed tickets online. I joined the line for people without tickets. It stretched all the way back to the end of the courtyard in front of the entrance, with lots of zigzagging. It looked formidable, but I timed it and it literally took me only 10 minutes between when I joined the line and when I entered the cathedral. Once inside, you can take as much time as you like.

Wonderful suggestions above. Since you will be in the Marais, walking the Coulee Verte will be close and is such a pleasure. Hopefully the weather will make it possible for you to enjoy fall in Paris outside in this lovely linear park.
https://en.wikipedia.org/wiki/Coul%C3%A9e_verte_Ren%C3%A9-Dumont

Have you checked out Rick Steves' Paris guide from your local library? - you will find great suggestions there.
Some of the following may not be considered "hidden" or "gems" -
Your preference is for WW2 history - but the Cluny museum for medieval arts and tapestry is worth a visit
The Carnavalet museum
The Picasso museum
The Jacquemart-André museum
The Hotel de Sully in the Marais yard & garden as access to the Place des Vosges
Deportation Martyrs Memorial on the tip of L'Ile de la cite behind Notre Dame (free)
St. Eustache church
Attend an evening concert at Sainte Chappelle
St Pierre de Montmartre church - just steps from the basilica

I did a different tour in August, but Bike About Tours offers a "Hidden Paris" itinerary. I enjoyed seeing the city from that perspective and felt perfectly safe (you aren't riding in major traffic). https://www.bikeabouttours.com/tours/hidden-paris/

Hello,
We spent a week in Paris last year on our second trip and were looking for hidden gems as well. Our favourite museum was the Museum of Fairground Arts. You have to book a timeslot tour and they tell you it will only be in French, but our guide translated everything for us and was wonderful. It is all art, animatronics, carnival games, and rides/carrousels from the 1800 and 1900's. It was so fun playing the games and riding the beautiful old rides. Every time we thought we had seen the last room, there was another section with even more impressive objects.

And our second surprising find was a small group walking tour through Montmartre, which traced the steps of artists. (https://www.airbnb.ca/experiences/925064). We learned so much and this was our best guide/tour from an entire summer of travelling.

Have a great trip!

Just did the Liberation museum at Denfert Rochereau right across from the Catacombs entrance today -- very interesting, free , and the stairs down into the bunker and back -- well I may decide to take a pass on climbing the Notre Dame Tower again as those stairs were a lot. Reminds me I am getting really old.

There are a lot of little visited museums. Balzak, Victor Hugo, Montmartre, Marie Curie or even better known but still often overlooked spots like Jacquemart Andre and Malliol. We went to an amazing photo exhibit at the Malliol last spring.

I would get a good Paris Walks type book with curated walking tours and try those that interest you catching 'hidden gems' along the way. We particularly like the architectural walk in the 16th in the old Frommers 24 Paris Walks book which is available used on line.

Butte Aux Cailles is interesting and there are a number of interesting walks below Tolbiac including Cite Floral. But a walking map/guide is useful there so you know what you are seeing.

I like to go to the major parks. On the far side of Parc Vincennes is the remains/ruins of the human zoo where people from the colonies were put on display during a turn of the century world's fair -- it was all the rage around the workd in the early 1900s.

And dozens of great day trips to towns, chateaux, etc near Paris -- for a lesser known but stunning grounds, we enjoyed a day trip to Maintenon Chateau.

Some great suggestions above- if you go to St Eustache don't miss the Keith Haring triptych. Two others which have not been mentioned yet:

1- Musee du Quai Branly- fascinating collection of art and artefacts from cultures around the world (a sort of anthropological museum)- https://www.quaibranly.fr/en/

2- Serge Gainsbourg's house- set up as he left it, with an audio tour by his daughter Charlotte- but you need to book this way ahead so might not still be available

Not a museum, but if you want something different, and a souvenir you'll use for the rest of your life, visit the small cutlery shop Laguiole en Aubrac. It's one of the very few traditional shops, where everything is made by hand and the masters sign each piece with their own pattern. Pick up a kitchen knife, hunting knife, or even just a pocket knife. If you ask they'll tell you about who made them and what's special and unique. The French have a long history of exceptional knife making.

If you're there after 5 OCT you may want to get tickets to the Theater des Varieties show "Arsene Lupin".

Also highly recommend Carnavalet. Not exactly hidden but as a free attraction some may be inclined to give it a pass. Their loss, it's actually superb.

Jacquemart-André is wonderful. If you speak French (or rather if you understand spoken French very well), book a guided after-hours tour. I think there are some tours in English during regular hours.

Someone mentioned Canal Saint-Martin. IMO this is a good place for a quiet stroll. Be warned that boat tours take up to 2.5 hours and go through multiple sets of locks. The covered section near the Seine is spectacular, but we found the second through umpteenth sets of locks tedious. There is at least one tour that skips half the locks, takes about half as much time and includes the covered section. I'd opt for that one.

In addition to walking the Coulee Verte that I mentioned upthread, you can take stairs down from it to Arènes de Lutèce which is ancient Roman ruins that is a hidden gem.

Have a look at Paris Walks for walking tours.
I’ve done some of them, they are excellent.
They may have WW2 themed walks.
Take a bus or metro out to a far stop and have a look at non touristed neighbourhoods.
Fontainebleau, Chateau de Vincennes.
Versailles: not for the palace, but for the town, on market day.
The Pantheon if you haven’t already been.

Maison de Victor Hugo

Musée des Archives Nationales

Musée Cognacq-Jay

Musée des Arts Décoratifs

La Galerie Dior

Curie Museum

Maison de Balzac

Fragonard Perfume Museum

A WWII-related site I have on my "to-do list" for this next trip is the American Cemetery at Suresnes. As I understand it, transit is on the suburban lines of the Metro and is accessible for those with the Navigo Decouverte pass. I have not been so no personal experience either with the site or the transit. I do try to visit the Cemeteries run by the American Battle Monuments Commission. They are always so well-kept and this one I do not think is often visited.

https://app-azeabmcgovwpprod.azurewebsites.net/cemeteries-memorials/about-suresnes-american-cemetery/

https://en.wikipedia.org/wiki/Suresnes_American_Cemetery_and_Memorial

There is also a memorial to resistance fighters nearby as well as a fort.

https://en.wikipedia.org/wiki/Mémorial_de_la_France_combattante
https://en.wikipedia.org/wiki/Fort_Mont-Valérien

If you are on the right day of the week, the Paris Walks Right Bank WWII walk is really, really good. I've done it twice. I have not done the Left Bank WWII walk (well, I tried one time but the group was too large and the leader was not able to project her voice so I dropped off.)

There is also a non-WWII related site that might be of interest and that is the grave of the Marquis de Lafayette over which the American flag flies. Visiting hours are restricted so check to see if this too would work into your time in Paris.

https://en.wikipedia.org/wiki/Picpus_Cemetery

You've got LOTS of choices!!