The German town of Herzogenrath and the Dutch town of Kerkrade effectively form one large town with an international border running through it. This is the story of how this happened, what it meant for the people living there, and how the place functions today.
One doesn’t need a passport to change between Germany and Netherlands. In fact nobody cares at all is you do so.
You don’t need to show it, and an ID card suffices, but you still are legally required to have identification when you cross the border.