Since 1922, when a Cunard liner made the first circumnavigation of the globe, travelers have thirsted to follow in the path of early explorers to discover what's beyond the horizon. World cruises are a time-honored tradition that is being upheld by a handful of luxury and premium cruise lines. Roaming the globe, passengers can combine leisurely sea days with exciting overland tours to attractions such as the Taj Mahal, Iguazu Falls, the Great Pyramids of Giza, or an African safari, which all require multiple days ashore. Keep in mind that you will be spending a lot of consecutive days at sea and traversing mighty bodies of water, which often means three or four -- or more -- days at sea without land in sight. For that reason it's important that you select a ship that offers the ambiance and amenities to meet your expectations. Cunard's ocean liners are designed to handle ocean crossings, while the other lines' cruise ships that sail on world cruises are generally mid-sized and more susceptible to motion.