A castle watches over the meeting of two rivers. Perched on its spur above the Lahn, Burg Lahneck sets the tone as soon as you dock: this is where the Upper Middle Rhine Valley begins, a 65-kilometre corridor listed as a UNESCO World Heritage Site where fortresses follow one another from hill to hill all the way to the Loreley. Lahnstein, a twin town that grew up on either side of the river, offers a more intimate port call than its famous neighbours, with two castles within sight and a third, legendary one directly opposite on the other bank of the great river.

Burg Lahneck, Goethe's Castle

The climb to Burg Lahneck rewards the effort. Built in the 13th century by the Archbishop of Mainz to protect the border of his territory, the fortress has kept its pentagonal keep, its Gothic chapel and its rooms filled with wood panelling and suits of armour. Guided tours tell the house legends, from the last Templar to the young Scottish woman imprisoned in the tower. Goethe himself, travelling up the Lahn in 1774, was struck by the silhouette of what was then a ruin and dedicated his poem "Geistesgruss," the spirit's greeting, to it. From the terraces, the view plunges over the confluence and the town's slate roofs.

Oberlahnstein, Walls and Lanes

Below, the old quarter of Oberlahnstein deserves an attentive stroll. Entire sections of the medieval wall survive, punctuated by towers including the Hexenturm, the "witches' tower," with its pointed roof. The lanes bring together half-timbered houses, courtyards of former wine-growing farms and squares where cafés set out their patios on fine days. On the riverbank, the Martinsburg, the archbishops' toll castle, recalls the era when every barrel travelling up the Rhine paid its due here. The old half-timbered town hall is among the prettiest examples in the region.

The Marksburg, the Undefeated

Facing Lahnstein, on the right bank, a silhouette dominates the wine-growing town of Braubach: the Marksburg, the only hilltop castle on the Middle Rhine never to have been destroyed in seven centuries. The visit, guided only, takes you through a medieval kitchen, the knights' hall, the armoury and the cannon battery, in a state of preservation that sets the imagination running. Braubach itself, with its tightly packed half-timbered houses and flower-filled alleys, rounds out the excursion. The site can be reached in a few minutes by road from Lahnstein; many cruises organize their main outing there.

Between the Rhine and the Lahn

Walkers enjoy another luxury: the trails. The Rheinsteig, the ridge trail on the right bank, passes directly by Burg Lahneck, while the more secluded Lahn valley unfolds meadows and wooded slopes toward Bad Ems, the spa town also inscribed on the World Heritage List among the Great Spa Towns of Europe. Even an hour's walk along the Lahn is enough to change the atmosphere: the tributary lives at a more hushed pace than the great river.

Port Call Pointers

• Mooring along the Rhine; the old quarter of Oberlahnstein can be reached on foot.
• Burg Lahneck: a steady climb on foot or a short taxi ride; guided tours depending on the season.
• Marksburg in Braubach: about 3 km; guided tours only, stairs and uneven cobblestones, good shoes required.
• Koblenz and the Deutsches Eck are less than 10 km downstream.

Before Heading Back on Board

As the sun sinks behind the left bank, Lahnstein's two castles briefly blaze with light, then fade one after the other. The ship resumes its course along the river, and everyone keeps in mind this image of patient sentinels. Goethe needed only a single boat trip to write his verses; today's travellers leave with the same privilege: having seen the Romantic Rhine open up before their bow.