I would say Teylers Museum in Haarlem, the Netherlands:
Air and Space in DC. You can touch a fucking piece of the moon!
Probably Musee d’Orsay in Paris. It holds many of the most famous paintings ever. You can walk right up to each piece and get a close look. And it has several nice cafés where you can sit and have lunch or a coffee. It’s very chill.
By comparison, the Louvre is a mad house, the popular stuff is roped off, and the cafés are more like a snack bar.
If you’re into U.S. (pop) culture, I think it’s hard to beat the Smithsonian in Washington D.C. It’s got historic aircraft, movie props, costumes, etc. Fun stuff. And it’s mostly/all? free so you can spend the day going in and out, having lunch nearby in DC, seeing famous monuments right outside, etc.
