The best river cruises have always had a certain mystique that draws travelers from far and wide—even those who are new to cruising. For history buffs, they could be an excellent way to visit ancient sites or historical landmarks. For those that love the outdoors, river sailings are a way to experience the natural landscape of popular destinations that you might otherwise not get to see. With limited space onboard, river cruises often book up well in advance—so consider booking these once-in-a-lifetime voyages as early as you can.