In the United States, most Christians say that they observe Sunday, the first day of the week, at least in part, to commemorate the resurrection which they believe took place on the first day of the week. Does anyone know, in those areas of Europe that use a calendar that labels the seventh day of the week, “Sunday”, on what day they hold their weekly worship services? If they hold it on the seventh day, do they reject the first day as being a special day?

I don't know anything about the European calandar, but in Genesis, God rested on the seventh day. Maybe that is the interpretation that is happening in Europe, and it is still a special day. Just guessing here.