Two completely different things go by the name river cruise, and booking the wrong one is an expensive mistake.
One is a floating hotel. Seven to fourteen nights, a cabin, and full board. A fixed route out of Amsterdam or Basel, and a price in the neighborhood of a week in a good hotel.
The other leaves St. Goar at eleven in the morning, runs ninety minutes downstream, and costs less than lunch on board.
Most visitors who say they want a Rhine cruise want the second one. They just have no idea it exists.
The Boat You Actually Want
If the river is the whole trip, take the cabin ship. You unpack once, wake up somewhere new, and somebody else handles every decision. It suits people who want the Rhine and the Danube in one go, and anybody who would rather stop moving luggage.
If the river is one day inside a longer trip, take the scheduled boat instead.
Between Cologne and Mainz these run daily from April to October and call at more than thirty landing stages. Buy a ticket at the pier, get off wherever you feel like it, and take the train back. No booking, no cabin, no commitment.
That second option is the one nobody mentions to visitors, and it’s better value by a wide margin.
There’s a good piece of history sitting behind both. The Cologne-Düsseldorf line (Köln-Düsseldorfer, or just KD) was founded on 11 June 1826. Its first scheduled service ran the year after. The company later built the first purpose-made cabin ship on the river, working Basel to Rotterdam. That makes it the outfit that invented the river cruise.
Then in 2000 KD sold the entire cruise division, nine hotel ships included, to Viking River Cruises.
So the brand every American knows from twenty years of television bought its start from a Cologne shipping company founded the year before Beethoven died. ;-)
A Castle Every Mile
The stretch worth planning around runs from Bingen and Rüdesheim down to Koblenz. That’s 65 km, or about 40 mi.
Along it stand around forty castles, palaces, and ruins. Roughly one per mile, for forty miles.
UNESCO added the valley to the World Heritage list in June 2002. It was the first German cultural landscape to make it onto that list at all.
The castles were tollhouses. Every prince, count, and bishop who held a stretch of bank built one and charged the boats going past. That’s why they sit where they sit: low enough to watch the traffic, high enough to be awkward to storm.
Pfalzgrafenstein takes the idea to its logical end. It stands on an island in the middle of the river, and it was built for nothing except collecting money. No village to protect, no land to hold. A stone toll booth in the current.
Marksburg is the other one to know. It’s the only hilltop castle on the Middle Rhine that was never destroyed. So what you’re looking at is the real thing, not a nineteenth-century romantic rebuild. Plenty of the others are rebuilds, and they’re honest about it.
The narrowest point is the Loreley. The river squeezes down to about 130 m (roughly 430 ft) across. It drops to around 20 m (66 ft) here, the deepest spot in the valley.
Between St. Goar and St. Goarshausen you pass Rheinfels, Burg Katz, and Burg Maus, plus the rock itself. All of that inside 13 km (8 mi).
One honest note before you book a room with a river view. Freight railways run along both banks, all day and much of the night. From the water it’s part of the scene. From a hotel pillow it’s a factor.
Four Rivers, Four Different Trips
The Rhine takes all the attention. The others are separate trips with separate characters.
The Moselle is the slow one. It loops through vineyards between Trier and Koblenz, with locks the entire way. The slopes are steep enough that growers use monorails to bring the harvest down. Slow is the whole point.
The Main is the connector. It runs from Frankfurt through Würzburg and Bamberg, and a canal at the eastern end links it to the Danube.
That canal is how a ship gets from the North Sea to the Black Sea. It’s also how cruise itineraries reach Nuremberg, which sits on a small river no cruise ship could enter.
The Danube barely touches Germany before it leaves. Passau is where most itineraries start, headed for Vienna and Budapest. Regensburg upstream came through the war with its medieval core intact.
The Elbe runs through Dresden and Meißen and the sandstone country above them, then north to Hamburg. Fewer ships, fewer crowds, and a landscape that looks nothing like the Rhine.
The Neckar gets short boats out of Heidelberg, which is a good afternoon rather than a cruise. For everything else afloat, there’s German rivers.
Season, and What Can Go Wrong
The season runs April through October. Outside it most scheduled boats are laid up, and the cabin ships switch to Christmas market runs in December.
Two things interfere, and both come down to water level.
Low water is the common one. In a dry summer the Rhine drops far enough that loaded ships lose draft, and cruise lines start shortening routes or bussing passengers between ports. It happens some years and not others. It happens often enough that the fine print on your travel insurance is worth ten minutes.
High water does the same damage from the other direction. When the river runs high, the bridges sit too low to pass under and the ships simply stop.
Both are a reason to book the middle of the season rather than the edges. And to keep a second plan for one day of the trip.
While you’re picking dates: Rhein in Flammen (Rhine in Flames) runs every summer at five separate spots along the river, on five separate evenings. Castles floodlit, fireworks over the water, and every boat within reach sold out months ahead. Worth building a trip around, if the timing lands right.
One last thing, because the internet keeps getting it wrong. You cannot cruise the Rhine from Lake Constance. The Rhine Falls at Schaffhausen sit in the way, and no ship goes past them. Rhine itineraries begin at Basel or further downstream, and anything promising otherwise is selling you a map it hasn’t read. :-)
For the rivers themselves rather than the boats on them, start with German rivers. For the rest of the fortifications, German castles has thousands more.