Yes, you can leave Miami International Airport (MIA) during a layover, provided you have enough time and the correct entry documents. If you are a U.S. citizen or a domestic traveler, you can simply walk out of the terminal. For international travelers, you must first clear U.S. Customs and Border Protection, which requires a valid visa or ESTA. It is strongly recommended to only leave the airport if your layover is at least 6 hours long. This allows for roughly 1 hour to clear security/immigration, 1 hour of travel time to locations like South Beach or Downtown Miami via the "MIA Mover" and Metrorail, and 2 hours to return and clear security before your next flight. Miami is a very "layover-friendly" city because the airport is located quite close to the city center. However, traffic in Miami can be notoriously unpredictable, so always allow for extra time when returning. If your layover is less than 4 hours, it is best to stay in the terminal and enjoy the airport's many Cuban-themed cafes and shops to avoid the stress of potentially missing your connection.