From Trier we drove along Mosel, crosses the mountains towards Mainz, then turned around and started driving north along Rhein. The drive along Rhein was recommended by my brother, and was the main reason we made the detour rather then driving straight from Paris to Amsterdam. It was very much worth it: the hills surrounding this stretch of Rhein are covered with medieval castles. We counted 10-15, and according to the map we must have missed a few.