Yo, it looks like I get on the S8 Rhine-Ruhr S-Bahn train at Düsseldorf Hauptbahnhof and take it to the Wuppertal Barmen station...
http://en.wikipedia.org/wiki/S8_(Rhine-Ruhr_S-Bahn
Is it as easy as it looks?
And I guess the S11 train from the airport to the hotel is cheaper than a cab, right?
Düsseldorf Airport S-Bahn service
http://en.wikipedia.org/wiki/S11_(Rhine-Ruhr_S-Bahn