Pavillon de l'Arsenal

The Doll Museum is not in Montmartre, but in the 3rd near the Pompideou Center. It is closing on September 15th.

Oh, sorry, I always remember it as being in Montmartre. Thanks for the correction.

Let me chime in and say that the Pavillon de l'Arsenal indeed would be worthwhile for people who are even moderately interested in the history of Paris, including recent history, and why it developed the way it did. The disclaimer is that I'm a recently retired city planner, so I could have spent hours and hours there, but I see that others could enjoy it on a much more casual basis. Free and very convenient to Metro; there's a little gift shop too if you have a family member who is an architect or planner.

As a frequent Arsenal visitor, I've made great use of their book shop with its wide selection of books on Paris architecture. There is a particular set of books I like that details Paris architecture arrondissement by arrondissement.

If you like architecture it's also worth visiting the Cite de l'Architecture et du Patrimoine in the Chaillot Palace. They specialise in plaster casts of parts of famous buildings elsewhere in France, which might sound dry and "inauthentic", but the casts are incredibly detailed, life-size, and spectacular.

Here's a link to the info about the climbing wall:

https://www.timeout.com/paris/en/things-to-do/free-13-metre-climbing-wall-inside-pavillon-de-larsenal