The world's largest cruise ship has begun its seven-day maiden voyage from Port Miami - carrying nearly the population of a small city onboard. The Royal Caribbean's Icon of the Seas set sail today on a seven-day island-hopping voyage in the Caribbean before returning to Miami. The $2 billion ship runs nearly 1,200 feet (365 meters) from bow to stern and has 20 decks, 2,350 crew, 2,805 staterooms along with room for 7,600 passengers.