The Mushroom City-Metro International Airport (or simply called Metro International, IATA code: MKM) is an international airport located in the Mushroom Kingdom. It is the main airport in the kingdom, which serves the entirety of the country. (particularly Mushroom City).
It has an appearance in SMG4: Mario's Illegal Operation, where Francis drove Mario and his friends to meet and greet Saiko one last time before she departs to Japan. Oddly enough, Francis' limo drove on the runway, where most planes take-off and land there. It is possible that the limo was on the runway because the airport wasn't so busy at the time.
It makes a reappearance in SMG4: The Mario Showdown. It was at the time that the anime ban is still in full effect, where SMG4 and his friends were denied entry by guards Chris and Swagmaster at immigration and were told to fly back to Japan, because of the presence of Saiko, who is anime. When it took too long to be denied entry, Axol begins to draw anime characters that would be used to distract the guards, making their escape possible. After exiting the arrivals area, the gang stole a bus from the airport and rode to the city.
The airport itself seems to be very small despite the fact it is an international airport. It has two hangars, one runway and a terminal with 3 aerobridges with an Air France jet parked at one of them. An Air Traffic Control (ATC) tower is seen at the back of the terminal. There is also a highway connecting the airport to Mushroom City and to other parts of the surrounding areas.
Gates at the airport are marked from B1 to B3. From the concourse, passengers arrive at the immigration and customs area, with a statue of a macho man holding a globe. When the anime ban was in effect, passengers are checked to make sure that they were not bringing anything anime-related. Living anime beings were also denied entry into the country, and they would be ordered to fly back to their point of departure.
Outside of the arrivals area, there is ground transportation provided for passengers to get to the city centre, usually in the form of buses. There is also a parking area just outside the transportation area as well.
...and many more European, American and Asian destinations.