I first visited Germany when I drove around Europe back in 1996, where I put my car in a lift to park on the roof a department store in Hamburg and I stayed in penthouse of a near deserted Youth Hostel in Lorrach.
I've also 'visited' Frankfurt airport on a number of occasions..
But more recently I spent a long weekend in Koln and Bonn. The star attraction of Koln has to be the Cathedral, I first saw it from the train as I was passing between Frankfurt and Utrecht, and decided to come back for a closer look. There is nothing anywhere near as tall as it for miles, so no matter where you go in the city you can see the twin spires.
If there was one disappointment it would be that there are no old buildings left around the Cathedral, however the bombing in the second world war destroyed all them. But at least the Cathedral survived intact.
Bonn is only a short train trip from Koln, and has a much more laid back feel to it. It is based on the Rhine, just as Koln is, and is the birthplace of Beethoven. The tourist authority have a short walking tour that covers all the places of interest. I went to see the Arithmeum, which tells the story of adding machines, from the abacus to the computer.
I also took the Metro out to Konigswinter, and took a cog railway up to a look out point over the Drachenfels Mountains, and the Rhine.