The cathedral was even prettier than the castle, which was nice enough of its own accord. The above photo is of the outside--part of it. It's in the middle of Prague's castle district, surrounded by tons of other buildings, so I couldn't back up far enough to fit the whole of the outside into one photo.
The inside of the cathedral, to give you a vague notion of how big it was.
Zoomed-in photo of the stained glass at the far end. Tickets were required to go about thirty or forty feet past the entrance, so I didn't bother. There was still plenty to see, particularly the stained glass. I genuinely can't think of any stained glass I've ever seen that might be prettier, or as pretty, as the enormous, twenty or thirty foot tall windows in that cathedral.