Konstanz is a German city that behaves like a Swiss suburb: the border runs through the built-up area at Kreuzlingen, and the crossing is the only part of the journey that can genuinely surprise you.
It is a Schengen internal border, so there is normally nothing to do but drive through it. Normally is not always — spot checks happen, and they happen most on a Friday evening and a Sunday. Everyone in the car should have a passport reachable rather than packed.
