Jen Santos
Google
Definitely get tickets in advance and consider an audio guide so you can move at your own pace. The collection is varied, comprised of many portraits, frescos, a Brueghel, maps, globes, china, weapons, and music.
We went solely to see Beethoven's Eroica. It is on display as well as a Haydn manuscript dedicated to Mozart, Schubert, Strauss, etc. A few pages of sheet music are digitized for browsing: more of that would be appreciated!
We had a package with a mini-concert: that was very well done. The view of Prague from the balcony is breathtaking.
In sum, there's a little something for everyone, but getting here can be a challenge unless you are young and fit: it's a long walk over very uneven cobblestones.
P.S. If you get a bathroom code, don't forget the # or * after the numbers!