We had an apartment in Berlin so this was the first place we took her. Our kids were in college so we could go for a few months. In those days we had to change planes in Frankfurt due to the Berlin wall. It was a long trip, 10 hours. We fed her well the day before and as she was small she was at our feet in her carrier on the plane. I snuck her out a few times for love and water and she was perfectly fine. We found some out of the way places at the Frankfurt airport for her to take a pee. It is a short flight from there to Berlin so we were home free once we arrived. Of course in those days there were soldiers with machine guns all over the airport in Berlin.
Europeans travel with their dogs more than the US and though I will give you many great places to stay with your pet ,there are accommodations for all price points all over Europe. In the US it's either the lowest of the low places along the road or a few great hotels in big cities. There are some exceptions but this is the rule. More later.