Nintendo's 3DS pocket-sized game system includes "Streetpass", a method of sharing your high scores, Mii avatars and other game information with random strangers who also have 3DS systems. That includes the levels designed by Super Mario Maker, which are a few megabytes apiece.
The swap happens anonymously and automatically whenever two 3DS systems (which both have to have the feature turned on) are near to each other. The range is around 80 feet, depending on local wifi conditions.
Don't worry if you can't make your rendezvous; Nintendo helpfully set up 29,000 "Nintendo Zone" wifi stations that can store your steganographic content for you.