Venice, Dubrovnik, Miami - ports like these are visited every day by several cruise vessels, disgorging thousands of sightseers who land for a mad race to beat the queues and see the most.
But travellers on an expedition ship will experience virtually the opposite - landing in places that may not even have a proper harbour.
Instead they encounter wild animals and pristine nature.
Experts say this segment of cruise travel is growing, even though the cost of such a voyage can easily match that of a new car. Here's the low-down.
WHAT IS AN EXPEDITION VOYAGE?
Daniel Skjeldam, head of the Norwegian cruise shipping line, has a simple explanation: "In classical cruise travel most of the action happens on board. With an expedition cruise, the experiences that take place off the ship are the most important." For Isolde Susset, expedition travel chief of the German line Hapag-Lloyd Cruises, says it is the out-of-the-ordinary route that characterises such travel: "We're talking about adventurous cruises with the character of a student field trip."
Besides that a voyage might not always have a clear-cut schedule.
Skjeldam and Susset stress the importance of lectures on board and having expert guides for excursions.
Biologists, glacier scientists, and historians can give lectures or provide expert accompaniment when travellers go exploring a destination.
WHICH SHIPPING LINES OFFER SUCH CRUISES?
By its own account, Hurtigruten is the largest operator worldwide in this segment. Besides classic voyages along Norway's shoreline it also plies the waters of Antarctica, Greenland, Spitzbergen, Iceland, Canada and the Amazon region.
The Fram, Spitsbergen, Midnatsol and Nordstjernen - are in use for such expeditions. Among other shipping lines offering expedition cruises are Ponant, Poseidon and Lindblad Expeditions.
WHICH ROUTES ARE PLIED BY EXPEDITION SHIPS?
Antarctica immediately comes to mind. But then there is the Arctic and the South Pacific.
According to Helge Grammerstorf, national director of the German chapter of the Cruise Lines International Association, it is Antarctica and the Arctic that all expedition cruise companies regard as their classic destinations.
WHAT DOES AN EXPEDITION CRUISE COST?
An expedition cruise is expensive. At Hapag-Lloyd Cruises, for example, a 22-day Antarctica voyage starts at $20,000. The reasons for such a high price, according to Susset, include the lengthy duration of a cruise and the low number of passengers with a comparatively large crew.
Planning a route is costly, and there are environmental aspects - for example, ships may only be powered by diesel, and not by heavy oil, in Antarctica.
WHO ARE THE PEOPLE WHO LIKE THIS KIND OF CRUISE?
Not surprisingly, given the expense, in general the travellers are affluent. And, with the voyages so long, they are on average older, according to Susset.
Skjeldam says there are two target groups for Hurtigruten: "People who already have seen a lot and want something completely special, and those who have saved up a long time for such a voyage and are fulfilling a life-long dream."
WHAT AMENITIES DO THE EXPEDITION SHIPS HAVE TO OFFER?
It is easier to list what the ships do not offer, says Skjeldam: "We don't have a casino, no climbing wall, no 15 swimming pools." By contrast, what is important is having great views of what is happening outside the ship. And, expedition ships are relatively small. The passenger numbers on Hurtigruten ships range between just 130 up to a maximum of 500.
WHAT ARE THE TRENDS IN EXPEDITION CRUISE TRAVEL?
"Previously passengers were primarily keen on seeing the spectacle of nature," Skjeldam says. But that is no longer enough.
"They also want to actively take part - with motor-boat excursions, hiking, or similar activities."
Voyages with a socio-environmental awareness are also in demand. For example, there are trips where passengers help to clean up the beaches of Spitzbergen.