Originally Posted by
stifle
To add to the above, make sure you don't discard your ticket immediately upon arriving at Düsseldorf airport station as you'll probably want to take the inter-terminal transit, which is not free although it's included on any rail ticket.
Well, that shouldn't be necessary - while the train is technically part of the VRR fare system, I have never encountered a ticket check on the Skytrain, nor have several airport employees to which I have talked about the topic (and they should be on that transit every day). Another problem is that there is no DB ticket machine in the terminal building, only a Rheinbahn machine which doesn't sell tickets for journeys exceeding the VRR borders which would technically require you to buy several tickets at higher prices than a combined DB ticket from the long distance train station would cost. To be honest, I've never had a valid ticket to travel from the terminal to the train station, and I've never gotten into trouble.
Ah, and something more: If you are on tight connections and need to buy a ticket at the train station, be sure to be one of the first people (no - be the first) to get off the Skytrain and hurry - I mean it, hurry - towards the station, as there are only 4 ticketing machines available for the whole bunch of people getting off the Skytrain - and expect a majority to need more than 10 minutes to get their tickets out of the machines, as most people there don't know how to handle them.