Watch Europe unfold before your eyes on a river cruise vacation

You’ve probably seen the pretty ads of long flat ships slowly cruising along the rivers of Europe. On the calm waterways, these vessels take travelers to such exciting cities as Vienna, Paris and Amsterdam; medieval towns; and hills covered with vineyards and castles where you might imagine a Rapunzel or Sleeping Beauty residing.

Beyond the scenery there’s another reason that vacations on these ships are so popular: They are easy. Much is prepaid and preplanned. The pace allows you to see key sights while you relax, traveling on such legendary waterways as the Rhine, Danube and Seine. The crew is there to pamper you.

What do I get for my money?

Expect to pay more than you would on a major cruise line. Most of the companies mentioned in this story charge upwards of $2,000 for a weeklong river sailing compared to about $1,000 for a European cruise on an ocean liner.

But you also get a lot for your fare. On major lines such as Viking River Cruises (by far the largest company on the rivers with market share nearing 50%) AmaWaterways, Uniworld, and Avalon Waterways, you pay upfront for a trip that includes comfortable accommodations, good food, wine and beer with lunch and dinner, organized group tours, and free Wi-Fi. Uniworld's all-inclusive fares even include open bar and gratuities for all onboard and shore activities.

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What are the ships like?

Keep in mind, river ships are much smaller than ocean liners, carrying a couple hundred passengers compared to thousands. Some have pools but don't expect water slides and climbing walls. Public areas may be limited to a lounge where everyone gathers at cocktail hour, a sundeck, a library and a spa or gym.

Companies vary when it comes to factors such as decor (Viking's streamlined look is suitably Scandinavian while Uniworld's is glitzier) and passenger activity levels.

AmaWaterways has a complimentary wellness program, complete with onboard instructors, and bikes that guests can check out when the ship docks. Avalon offers a series of Active & Discovery itineraries that allow passengers to opt for a bike or jogging tour one day and then go on a culinary or cultural excursion the next.

What kind of crowd can I expect?

Though most of these companies' customers are Americans, ages 55 and up, you’ll find much older and slightly younger folks onboard, too.

It's not all the AARP set: Some lines specifically target younger adults and families. Uniworld’s U River Cruises caters to cruisers between 21 and 45, marketing its ships as "part boutique hotel, part yacht, part local hotspot."

Adventures by Disney goes after family travelers with child-friendly tours and activities (on chartered AmaWaterways ships). Luxury tour operator Tauck hosts both adult-oriented sailings and Tauck Bridges itineraries designed for multigenerational families.

While river cruises can generally be both casual and upscale, ocean line Crystal Cruises entered the European river market in 2016 with the goal of being the most luxurious The brand’s stunning new all-inclusive ships are decked out with glass-ceilinged conservatories and suites serviced by butlers.

Where will we go?

The two most popular rivers are the Danube and the Rhine.

Danube: Standard one-week Danube itineraries, such as Viking's Romantic Danube and Danube Waltz cruises, concentrate on the area between Budapest and Germany’s Bavaria, with stops in Hungary, Slovakia, Austria (including Vienna and the Wachau Valley wine region) and Germany. Uniworld's Authentic Danube tour keeps the focus on Austria and Germany, traveling from Nuremberg to Vienna.

There are also holiday-themed Danube itineraries, such as AmaWaterways' Iconic Christmas Markets Tour and Dashing Through the Danube from Uniworld's younger-skewing U brand.

For something more exotic, Dracula fans might consider Viking's Passage to Eastern Europe tour. This lower Danube itinerary travels between Budapest and Bucharest, with an optional three-day extension that allows you extra time to explore the haunts of Romania’s Vlad the Impaler, the inspiration for Bram Stoker's fictional blood-sucking character. The standard cruise also takes you to Croatia, Serbia and Bulgaria, where you may learn about life at war and under Communist occupation.

Rhine: These journeys, including Crystal's Romantic Rhine target the regions between Amsterdam and Basel, Switzerland, taking you past famous castles and other picturesque sights.

The Rhine also gets its share of speciality seasonal tours: AmaWaterways and Avalon both offer Christmas market tours and Tulip Time cruises through the Netherlands and Belgium in the spring. Tauck provides a Yuletide cruise as well as an Oktoberfest edition.

Seine: Cruises from Paris to Normandy, such as Tauck's Impressions tour visit Versailles, Joan of Arc’s Rouen and the D-Day beaches. Their cruise also includes an exclusive treat for art fans: a visit to Claude Monet's home in Giverny.

On sailings from Bordeaux, on the Gironde and Garonne rivers, sipping fine wine is very much part of the scene.

Will I like it?

Introverts and loners, consider yourselves warned: River cruises are very much a group experience, and due to the small size of the ships, there’s nowhere to hide.

The experience is a lot like staying in a small boutique hotel, only it floats. It’s a very social environment where you’ll quickly get to know everyone thanks to the open seating in the main dining room. (However, Crystal and Avalon have begun incorporating more two-seater tables as part of their efforts to entice more young customers.)

Some will love the slow pace – going through locks on the rivers, taking walking tours onshore and partaking of more elaborate shore experiences (sometimes for a fee) with local guides.

A note to DIY types: Since you’ve basically signed on for a packaged tour, you'll want to look at itineraries very carefully to make sure there is enough time to explore on your own. On the plus side, the ships often dock right in town, making access easy.

But what's not to like about floating while watching the ever-changing scenery?

This article originally appeared on USA TODAY: European river cruises: Your guide to the major companies and routes