I liked Frankfurt. Its a clean, modern city. I don't speak German, so was a little lost. Found a nice gay bar in the triangle and spend the evening. Guys there were humpy and butch.
I had a little difficulty understanding how to pay for my drinks. The bartender kept giving me little pieces of paper. The place was so dark that I couldn't see that they were receipts that I had to bring to a cashier. Of course, I was assuming that the bartender was keeping my tab; not so. Anyway, fortunately I did have them all stuffed in my pocket, and figured out how to pay.
Took the train to Heidelberg - a beautiful medieval town, if you have the time. Lady running the public restroom turned out to be from the next town over from me here in Pennsylvania.