I've always gone to Prague & CZ in the summer but I'll be going in February. Ilja - I hope you chime in as your suggestions have always been great! Would Plzen be good to visit in winter? Any other ideas for day trips in winter? I've been to Terezin, Cesky Krumlov, Olomouc. Didn't know if the castles in the southern part of the country are open in winter as well as wineries. Brno might be an option too although I've been but my son who will accompany me has not been there. Thanks for any winter recommendations. He will be studying in Prague so I'll gather suggestions for him too February - May.
I'm visiting in March and am surprised how much the country is "closed" for the winter outside of Prague and Kutna Hora. An exception is Karlštejn Castle has one section/tour open.
Anyway, for Plzen the cathedral and the synagogue are both closed to tourists February and March. I think the cathedral tower is open, I can't remember, decided with main sites closed to not visit. The brewery is open but I'm not interested.
Tom_MN good point about seasonal closings. It looks like the castle you mentioned is just open Friday - Sunday when we are there. That makes sense. I sent you a private message of an itinerary I had two summers ago throughout the southern portion of the Czech Republic from Brno to Prague. Again, I'm not sure what's open in March but it might give you some ideas if you venture out of Prague. Thanks!
I think that travel in Czech Republic in winter has only one advantage - fewer tourists. Wait - maybe also the absence of oppressive heat. Bigger cities like Brno, Ostrava, Plzen are still somewhat alive.