*gasp* You are in Düsseldorf? I had no idea that "this FedCon" you were tweeting about is taking place right here. Anyway, Düsseldorf isn't spectacular but it does have nice spots, e.g. along the Rhine or the many japanese stores and restaurants near the main station. There are also a lot of good museums. I'm trying to come up with something geeky but draw a blank :( Depending on how much time you've got I recommend going to Köln/Cologne (30min by train) and at least see the cathedral. It's a touristy thing to do, but the cathedral never fails to awe me. You probably get this all the time, but for completeness's sake: If you'd like a native guide, I'd be happy to show you around. Also you're welcome to my internet anytime ;)