The cruise industry will tell you not to worry about rough seas—and you'd actually do well listen to them. It's not in their interest to take passengers on a ride that has the potential to make some people seasick. So most cruise lines program itineraries on waters that they can count on: predictable seas that their ships can handle and easily steer clear of brewing storms (often to the point of changing ports of call in the case of cruising the Caribbean during hurricane season). That's not to say that bad weather can't crop up unexpectedly, but cruise lines do their best to avoid turning their ships into bucking broncos at sea.

However, there are a few waterways in this world that naturally have rougher seas than other passages. Educate yourself on the itineraries that can be rough and then decide if the allure of the voyage outweighs the potential for some tossing and turning.