At the risk of stating the obvious, an around-the-world cruise requires a significant investment of time, usually around 140 days, or slightly more than four and a half months. The advantages of such an odyssey, as opposed to a comparatively brief fling on a private jet tour, are numerous. Rather than packing and unpacking every two days, travelers on a ship settle into their suite and adapt to life in their temporary home. Even the smaller ships that make a circumnavigation accommodate more than 350 passengers, so congenial company is not too hard to find. And in the numerous ports of call, the leading cruise lines arrange an amazing number of excursions — sometimes 10 or more at each stop — that cater to every taste, age group and level of fitness. If travelers take advantage of all the opportunities on offer, they will see and learn an astonishing amount. Of course, on a world cruise, as opposed to those that hug the shorelines of the Mediterranean or progress through the islands of the Caribbean, a significant number of days are spent at sea, with just a view of an endlessly receding horizon.