If you are flying to Schwerin, the nearest international airport is Hamburg. From here, you should take a train to Hamburg Hbf, where you can then take another over to Schwerin. The journey will take around an hour and three quarters from the airport.
Schwerin is also easily accessibly by rail, with services running direct from Berlin, or some may require a change at Hamburg.
Once in the city, bus numbers 1, 7, 12, 19, 14, 2, 5 8 and 19 all pass by the Freilichtbühne Schwerin. The festival is also just a 25 minute walk from the city's main train station.
Minimum age of entry is 18.