Upvote:1
Define "reasonable".
The distance isn't a problem, road conditions shouldn't be either (but don't expect US style superhighways) except some parts maybe in winter (snow and icing).
It's possible that there could be rental agencies disallowing entry in their vehicle into Poland due to some reports of car theft gangs operating out of there, but I seriously doubt it's much of an issue any longer. (It's not clear if it's still an issue, and most of the reporting on this problem suggested the cars were stolen outside Poland, then trucked there later for disassembly).
So there's no reason you shouldn't be able to do it.
Upvote:1
Use one of the bigger car rental companies. Usually you can rent a car in Germany and return it in Poland. Then stay for some days and get a car to return to Germany. Shouldn't be a problem in every bigger city.
You need a drivers license that is valid in the EU!
Upvote:8
Absolutely.
It's just a short ride, 5Β½-6 hours. As for quality of the roads, in both in Germany as well as in Poland you'll be riding top quality freeway practically all the way. They are basically equivalent to US Interstate Highways.
In Germany it's Bundesautobahn 15 (Federal Freeway 15), in Poland short part A18, then A4. All of which are recently (re-)built.
You don't even have to worry about snow or ice in the winter, these freeways are part of one of the main pan-European routes, they're considered priority one for deicing.
Keep in mind that the only reasonable option for parking in KrakΓ³w will be paid underground parking, which should cost you around 50zΕ (about $16) per day.