Guidebook will thrill you
If you have a guidebook (I used the Eyewitness Guide to Prague)- the info you can get on every facet of this castle is great. It has so MANY chapels inside, and you will enjoy the detail of each one, if you have a little explanation. And you go down into the catacombs of the cathedral too. Very neat. Alfonse Much created a huge stained glass window in one chapel (he was one of the Czech Republic's greatest artiosts), and it's worth the trip. Just outside the cathedral is ONE (of like 2) free restrooms in Prague. The ticket was kinda pricey, and photos are hard to take in there, but its a nice place to spend an hour.