Travel to FreiburgBy plane to Basel
The nearest airport is Basel which is fairly well connected with public transport (traveltime: around an hour) to Freiburg - either by a bit unregular direct bus to Freiburg Main Station (https://www.freiburger-reisedienst.de/index.php?lang=en) or via regular local bus to Basel Main Station (https://www.euroairport.com/en/passengers-visitors/access-parking/access/bus.html) and from there with the train.
By plane to Frankfurt
Frankfurt is also a good option. There is a high speed train connection (during the day at least every hour - traveltime: a bit more than two hours) directly from the airport to Freiburg (https://www.bahn.com/en/view/index.shtml).
Freiburg is well integrated in the European high speed train network.