It worked yesterday and today around 2:30 pm. I have been a heavy user of it for about two years, now it has become a very rare occasion. I am still scared

Bonn vs. Duesseldorf? Tough one... They both have their charm. As I haven't spent enough time in either one of the cities but I think, I have seen more of Duesseldorf, I would go for Bonn.
Also, Brühl was a nice suggestion. I study in Brühl these days and I passed the castle a few times but never made it in. Yes, I feel ashamed of myself but I will try my very best to see it at some point.

Send me PM if you are interested to have a beer in CGN at some point.