The South American giant conjures up all sorts of images — impenetrable jungle, dangerous animals, Amerindian tribes, and lost civilizations. The reality of a cruise along the Amazon is a fascinating journey through different cultures and even more diverse flora and fauna. Containing more water than the next seven biggest rivers combined, the Amazon can at times seem more like an ocean than an inland watercourse. It's also long: more than 4,300 miles from its glacial source in the Andes to the equatorial Atlantic. Most cruises are based out of Manaus (Brazil) or Iquitos (Peru) and sail year-round during a high-water (December to May) or low-water (June through November) season.