Let us take you on a journey along the Rhine in a river cruise that sounds so relaxing, you'll be booking your fall travel plans.

161005RhineCruise mainI'm laying on my bed, gazing out the wall-to-wall windows when I spot the first one: A stone castle perched high up on the riverbank. It looks derelict and unoccupied, yet I feel a rush of excitement. I imagine a time centuries ago, when it would have served a purpose here, guardedly watching vessels ply the busy waters of the Rhine when this was the main travel route between southern and northern Europe. Another lingering look and then it's gone. Our ship, heading downstream, has left the castle behind, and with it any imaginary flaming arrows that might have emerged. But now I'm standing in front of the open sliding glass door so I can lean out, breathe in the fresh spring air and take in the sights. Best yet: I know more castles are on the way.

I'm on a journey from Frankfurt to Amsterdam with Avalon Waterways, and I've fallen in love. Once unperturbed by hopping from city to city, heavy backpack strapped around my hips, I've grown lazy as I've gotten older—perhaps just tired from a long winter of hard work—and I'm learning to appreciate the unpack-once, see-everything mentality of the cruise set. But the beauty of the European river cruise is the small scale of it all: No monster boats, these ships are sized exactly to fit under bridges and into the locks that raise and lower them between sections of rivers and canals. My ship, the Avalon Expression, is about as big as they can get: 135 metres long and 11.5 metres wide, with just 83 passenger rooms and suites. The result: An intimate experience where you can relax as you get to know a different side of Europe.

The Rhine in its entirety flows more than 1,000 kilometres from the mountains of Switzerland to Holland and the North Sea, but we're focused on one particular section: the Rhine Gorge, the 65 kilometres from Rüdesheim in the south up to Koblenz, where the Rhine joins up with the Moselle. A UNESCO World Heritage Site, this part of the valley is breathtaking, especially when seen from the water: tall, steep banks rise up from the river, alternately cloaked in tidy vineyards and dotted with castles, some 40 along the way, and interspersed with 60 towns and settlements. The Romans first built a fort in Koblenz more than two millennia ago, while the first grapes were being planted, and castles were being constructed about a thousand years later. On the water, away from highways and power lines and other trappings of modernity, it's easy to feel a link with that past.

Besides that, the towns are charming and well versed at welcoming visitors. In Rüdesheim, for instance, we photograph the storybook buildings and tour the eccentric yet earnest museum of mechanical musical instruments. Then we settle down in the warm May sun for mugs of heartily spiked Rüdesheim coffee, the brandy and sugar set aflame and topped with coffee, whipped cream and shavings of chocolate by nattily costumed barmaids. In Koblenz, we explore the narrow alleys and medieval churches and watch buskers sing in historic village squares while locals relax at sidewalk cafés. On a side trip up the Moselle to Cochem, we spot grapevine seedlings for sale outside shops and marvel at markings of past high water levels on buildings in the village centre, then climb the hill to Cochem Castle for a tour. Originally built about a thousand years ago, it was destroyed in 1689, then rebuilt in the 19th century, like many such structures, as part of the Romantic movement.

Our last excursion before disembarking in Amsterdam is Cologne. I dutifully explore its famous cathedral, admittedly stunning even for those who tire of too many churches. It's Germany's most-visited landmark, and its original construction took place between 1248 and 1473 before halting for close to four centuries until it was finally completed in 1880. The cathedral sees some 20,000 visitors a day, so I figure no one will miss me as I sneak out to the Birkenstock store to buy sandals at their only-in-Germany price—a steal even taking into account the exchange rate. That's the other beautiful thing about river cruises: There's room for independence, even on a scheduled itinerary. And so, retail therapy achieved, I return to join the group for ice cream on a sunny outdoor patio. I'm not in a hurry, after all.