Apparently there is a permanent exhibition, which ...

Apparently there is a permanent exhibition, which is the main part of the building and is free to enter, and another part with temporary exhibitions and such is paying.
We only accessed the free part and I must say that with that it is already worth visiting. Not only is it beautiful, but it also has interactive posters and screens that explain the place and its history, which surprised me and seemed wonderful (because it is the free part, too!).