I passed through Dusseldorf a few years back.
It seemed very quiet, and I had a good trek about the place.
Was planning a vacation for this summer and I figure it's between somewhere in Germany, or Prague (not sure about the latter as there don't seem to be any definitive zones. Though it is a popular destination).
I was considering Bucharest but I've heard there's less legitimacy and too many scams.
So Germany: Frankfurt (favourite so far), Berlin.........?
If there are any further updates from those who have done their homework?