There is an outlet center in Roermond, Netherlands. It is about an hour away from Dusseldorf and the only one in that area. I was in the Prada outlet store once or twice, but it's not really worthwhile ... and since I heard about the "made in China" tags, I'm not interessted to go there anymore.
Prada Outlet is in Austria (Parndorf), it's not far away.
Parndorf does have a nice Prada outlet, but it is about five hours away from Munich (it's on the "wrong" side of Austria). I don't know about Dusseldorf, but the only outlets close to Munich I can think of are Ingolstadt Village and McArthurGlen Salzburg and both don't carry Prada. Sorry!