Cruise lines are in a heated race to build larger and more lavish cruise ships. Royal Caribbean's "Wonder of the Seas," currently the world's largest cruise ship, has a staggering 18 decks and a capacity of nearly 6,988 passengers plus 2,300 crew members. That's roughly the equivalent of the population of Sedona, Arizona. These ships take years to build, and feature everything from ziplines to artificial surf machines, and actual neighborhoods full of restaurants, bars and stores to entertain passengers at sea.