This building in the middle of Gran Vía with Fuencarral always houses very interesting exhibitions with free access. I like it, not only because of how interesting the exhibits are, but also because of how well explained and prepared they are. I recommend stopping by to take a look when you're in the downtown area.
I love this place! All the activities they have always arrive in the mail and it is excellent how they promote knowledge of super interesting topics in a didactic way. With an excellent location and a tremendous super modern building, you can take a walk between Fuencarral and Gran Vía, a corner where this place does not go unnoticed. It has many free activities and some others that you sign up for prior registration, and they are very worthwhile. Recommended!
The Telefónica building is one of the most emblematic buildings on Madrid's Gran Vía. In addition, it has an exhibition area with several floors and most of them are usually free. The last time I was there, I was fascinated by the exhibition that they had mounted around the figure of the writer Jules Verne. It really was like moving into the world of the French writer. They also tend to have scientific displays where children can learn and have fun. Fully recommended if you pass through the center of Madrid.