The most spectacular stretch of the Rhineland is along the Middle Rhine, between Mainz and Koblenz, which takes in the awesome castles and vineyards of the Rhine Gorge. Highways hug the river on each bank (B-42 on the north and eastern sides, and B-9 on the south and western sides), and car ferries crisscross the Rhine at many points. Cruises depart from many cities and towns, including as far south as Frankfurt. Trains service all the towns, and the Mainz-Bonn route provides river views all the way.
The Rheingau. Though the course of the Rhine is generally south to north, it bends sharply at Wiesbaden and flows east-west for 19 mi to Rüdesheim. This means that the steep hills on its right bank have a southern exposure, and that vineyards there produce superb wines.
The Mittelrhein. The romance of the Rhine is most apparent in the Middle Rhine, from Bingen to Koblenz. The Rhine Gorge not only has the greatest concentration of castles, but also the storied cliff the Loreley.
The Mosel Valley. Koblenz and Trier aren't very far apart as the crow flies, but the driving distance along the incredible twists and turns of the Mosel River is 125 mi. The journey is worth it, though. The region is unspoiled, the towns gemlike, the scenery a medley of vineyards and forests, and there's a wealth of Roman artifacts, medieval churches, and castle ruins to admire.
Bonn & the Köln (Cologne) Lowlands. North of Koblenz, the Rhine is less picturesque, but it does shoulder the cosmopolitan cities Köln and Düsseldorf, as well as the former capital city of Bonn.