I'm flying into Dusselsorf at the end of July. I note that the viewing deck can only be accessed after a security point, does this mean only when you are actually checking in to board a flight, or can you go to visit and then leave the airport?
To answer my own question for anyone planning to go - the viewing area is accessed before you go through flight security/passports etc.. You have to pass through a simple security check to get onto the viewing area. The price is now €2.20.
The viewing platform at the station is closed permanently now.