Strasbourg, France
The best thing about travelling in hostels is that you get to meet people - nothing like sharing a dorm to get people to open up. I ended up hanging out with a Scottish physics student from Glasgow university, playing air hockey in the hostel basement - perhaps that's not everyone's idea of what to do in Europe, but it worked for me. Of course, my other roommate is a bit sketchy, and I have to be careful with where I leave my stuff, but I stayed a couple nights...