Cruising is currently the fastest-growing sector of the tourism industry, with 23 million passengers worldwide expected to sail this year. With almost three times as many new river cruisers as ocean-going ships being built, it's clear where the main interest lies. The numbers tell you why.

24 hours a day, 7 days a week
Unlike on an ocean cruise, on a river there is always something interesting to look at, all day, every day. Rivers were Europe's first highways and their routes link historic towns and cities, as well as picturesque villages. Even more conveniently, cruisers generally moor right in town centres so that all the sights are just a gangplank away.

360 degrees
Whether your cabin is port or starboard, you will always have a view, unlike on an ocean cruiser following a coastline, where you need to be lucky, or well-informed at booking time. Of course, it will still only be of one side, which is why most passengers spend their waking cruising hours upstairs in the lounge, or on the sun deck. Mind you, watching the passing scenery from your bed through a ranchslider is a delicious treat, even if the gentle motion means your eyes don't stay open for long.

180 passengers
Also unlike on an ocean cruiser, those passengers relaxing in the lounge, library or spa, working out in the gym, or snoozing in their staterooms do not add up to the 5000-plus on a mega-ship - that's the population of Dargaville - but usually number fewer than 180. This means an increased chance to get to know many of your fellow cruisers as you pass in the hallway, share a table in the restaurant or stand alongside each other at the bar. There's a friendly, intimate atmosphere, more like a club, where people are recognisable individuals rather than a mass of strangers.

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A cruiser winds its way through Provence. Photo / Supplied
A cruiser winds its way through Provence. Photo / Supplied
1:3 Crew-to-passenger ratio

This varies between companies and individual ships, but can be as high as 1:3, making real personal service possible. Don't be surprised to be greeted by name from the second day, or for your individual preferences to be learned and remembered by your waiter. Even the captain may have time for a friendly chat as you wander along the sundeck past the wheelhouse.

120m long
Most European river cruisers are a similar length and width (120m x 12m), the measurements dictated and limited by the height of bridges and the length of locks. There are three decks of varied accommodation, plus the sundeck, and many staterooms have ranchsliders with narrow verandas or balconies. Space within the rooms is at a premium, and much ingenuity is shown in the efficient arrangement of the necessary elements of bed, ensuite and storage. It's expected, though, that the cabin is primarily for sleeping, and that waking hours will be spent in the lounge or ashore.

15cm
This is the clearance under some ancient city bridges, built long before anyone thought of multistorey ships on the rivers. Heavy rain raising river levels can cause difficulties, even when the wheelhouse is retractable like a tortoise's head. Equally, lack of rain can mean that there is insufficient depth of water, so progress is affected. These small-print facts of river-cruising life can result in coach outings instead.

Visit Amsterdam on a river cruise. Photo / Supplied
Visit Amsterdam on a river cruise. Photo / Supplied
23 days

Most river cruises last a week, or two, but true aficionados will take the longest route from the Black Sea to the North Sea, up the Danube from Bucharest, along the Main and into the Rhine to finish at Amsterdam (or vice versa). This waterborne grand tour passes through nine countries and many centuries of culture and history.

10 months
Cruises take place year-round, except for in the depths of winter, with special seasonal focuses such as Christmas markets and Dutch tulip fields.

Zero
Extra charges for guided excursions and drinks on board are not usual on river cruises, making for a more carefree daily experience and a happier ending. Onboard wifi and airport transfers are often also included, and tips, too. (There is also zero chance of seasickness on a river.)

80m
This is the maximum distance you can trail behind a tour guide equipped with a radio microphone and still hear the commentary through your headphones. At each stop along the route a walking tour is arranged with a local guide, lasting an hour or two, to introduce you to the town and give you some background. It may include entrance to a museum or castle, refreshments or entertainment, and is an excellent shortcut to getting to know the place.

13 rivers
Cruises take place along all or part of the Rhine, Moselle and Main through the Netherlands, Germany and Switzerland; the Elbe through Germany and the Czech Republic; the Danube through Eastern Europe; the Rhone, Saone, Seine, Loire and the Bordeaux region rivers in France; the Douro in Portugal; and the Po in Italy.

3 cheeses
A different selection of cheese offered every night on Uniworld's Rhone cruise is an example of how regional cuisine and wines are made an integral part of some cruise experiences.

Dining aboard the River Beatrice cruise ship. Photo / Supplied
Dining aboard the River Beatrice cruise ship. Photo / Supplied
10PM

Local singers and musicians come on board to offer post-dinner entertainment; there are also daytime lectures on art and history.

50+
This is the age group of most river cruise passengers, weighted towards the older end for several reasons: they have the time and the money for such trips; they enjoy the ease of this type of travel; they have probably done the self-drives and independent travel already; and they are more interested in culture and history than entertainment and partying. However, with a little research it is possible to find family-friendly cruises.

8+
Companies offering European river cruises include Uniworld Boutique River Cruises, Avalon, Tauck, AmaWaterways, Scenic, APT, Viking and CroisiEurope.

$2500
This is the least you could hope to pay for a comfortable week on the Rhine, less for more basic conditions, or more than twice that for added luxury and extras. Your choice.