It's the big kahuna, and cruising's holy grail. A World Cruise is a big time commitment: Book one, and you're basically running away to sea for three to four months. Around the world cruises cater to affluent travelers with plenty of time on their hands — though you can also book smaller segments in many cases. Southampton, England, is a popular departure point, but sailings also depart from U.S. ports like Ft. Lauderdale, Miami, and San Francisco. You'll have plenty of sea days, as the ship continent-hops, and you'll often have more time in port than the typical cruise allows.