By train: Baden-Baden is served by the high-speed train lines Frankfurt-Marseille (TGV) and Zurich-Hamburg (ICE). Take bus line 201, 201E, 216, or 244 to bus stop Augustaplatz/Museum Frieder Burda, which is next to the conference site. There are more bus lines, some go instead to stop Leopoldsplatz.
From October 1 in German trains FFP2 masks are mandatory.
Note that 40% of German long-distance trains are delayed. When trains are out of schedule, it is advisable to consult https://www.bahn.com/en (or the DB app for your mobile phone) for alternative connections instead of waiting for your delayed train. Even if you bought your ticket for a particular train (instead of the flexible ticket valid on all trains), you can choose any train if the booked connection is seriously delayed.
By airplane: Airport Karlsruhe/Baden-Baden (FKB) is served by several airlines, including Ryanair. Take bus 285 to Baden-Baden rail station and change to the bus lines mentioned above. A taxi is much faster, but costs around 35€.
From Frankfurt airport (FRA) there are some ICE trains with direct connection to Baden-Baden. Most connections, however, require to change trains in Mannheim (on the same platform). The travel time is less than 90 minutes. Except for a few night-time trains all trains depart at the train station Frankfurt (Flugh) Fernbahnhof (for long-distance trains). If you arrive in Terminal 1, the shortest way to the train station is as follows: (1) Ignore the signs to the station (they guide you on a slalom tour through a food court in the basement), instead take the escalator up to the departure level. (2) Take the escalator (going up) between check-in halls A and B. (3) Now follow the signs to Fernbahnhof. If you arrive at Terminal 2, take the shuttle bus to Terminal 1, the bus stop is close to the rail station.
Public transportation from Strasbourg Airport (SXB) is quite invonvenient. A compromise is to take a taxi to the central bus station at Place d'Etoile and take a Flixbus to Baden-Baden.
