Start by naming any country that France borders. Then name any country that borders any of those countries. Then keep going until there are no more countries left to name.
I used cities from this quiz. In it, the Ruhr is filled but it represents an agglomeration without a main city. The same case is with Katowice. I thought to include them. All I can do is add type ins for cities which are included in their agglomeration.
done