Agree with #10. The night train from Warsaw to Prague felt very safe. And also rather empty, not sure if the issue was the price or all the horror stories about robberies.
Many companies offer an Auschwitz as a day trip from Krakow. I recall it usually being offered as a half day tour, often combined with the salt mine. Any hostel/hotel you stay at can book you on a tour. It's also perfectly doable on your own with the bus being an easier option since it stops right outside (train station is maybe a 10 minute walk). Just know the return times of the train/bus.
Also agree that Salzburg is a good day trip from Munich. I also enjoyed Augsburg (not saying it's comparable to Salzburg, just that it's nice).