Yes, if you are a U.S. citizen on a "closed-loop" cruise (one that begins and ends at the same U.S. port, such as Port Canaveral or Miami), you can generally visit Castaway Cay in the Bahamas without a traditional passport book. In lieu of a passport, you must present a government-issued photo ID (like a driver’s license) and an original or certified copy of your birth certificate. Children under the age of 16 usually only require their birth certificate. Because Castaway Cay is a private island owned by Disney, the disembarkation process is very streamlined; you typically only need your "Key to the World" card to exit and re-enter the ship. However, travel experts and the U.S. State Department strongly recommend carrying a passport anyway. If an emergency occurs while you are on the island—such as a medical issue or missing the ship’s departure—you would be unable to fly back to the United States from the Bahamas without a valid passport book, which could lead to significant legal and financial complications.