Originally Posted by
stifle
Doesn't solve the problem of getting from the airport to the train station, of course; the transfer train is not free.
Transfer train is free if you have a rail OR air ticket arriving/departing from Dusseldorf airport OR if you have purchased a ticket for the viewing terraces OR if you are airport staff OR various other exemptions. Pretty much if you're not a vagrant and have a legitimate reason for riding the train, you can ride for free.