The real question is - Why not travel Europe with a dog? Generally, Europe is much more dog-friendly than the US and it’s a great way to meet people and get an “insider” view into a city. You also see parts of the city through the eyes of the people who live there.
For example, I lived in London for about four years without a dog – and I saw the city in a whole new way when I travelled there with Fritz. One morning we went to Lincoln’s Inn Fields in central London. It’s around the corner from my old office and I used to go there all the time. But with Fritz it was different. We spent about two hours one morning – me talking to other dog owners and Fritz playing with other dogs. I discovered a great group of people who I would have never met without Fritz