Here's the Ten Best Cruises in the World

You may think of cruises as floating resorts, but plenty of ships help you get more intimately acquainted with ports of call.

National Geographic Travel announced its "21 Best Cruises in the World" in conjunction with its April/May issue of National Geographic Traveler.

From serene rivers to ocean voyages, the list features cruises that focus on specific regions, employ experts to add local insight, and can transport you to places that are otherwise hard to reach.