I am starting to plan my trip in mid-October and am interested in seeing some castles along the way if it works out well. I plan to travel from Paris to Berlin. A work friend has told me about Rhine River tours that allow you to hop on/off the boat and visit castles. I've done some searching on my own but haven't found anything like this.
Is there an easy way to make a day or two trip on the way to Berlin to see castles? I plan to only use train or airplane transportation on this trip.
If not I'll probably take a night train run by a Russian company from Paris to Berlin. It is ~100 Euro. Not too bad for lodging/transportation in one.