Yes, I can see why you'd want to visit the bridge. The 'devil's bridge' is an impressive construction. I would definitely take a car for this. It will leave you with far more flexibility and allows you to return via Dresden (and/or Meissen, if you are interested). Possibly even stay overnight in Dresden. The train is certainly possible, but I suspect will involve at least two changes and a bus and walking/taxi at the end. My guess, but check on bahn.de, this will take you at least three hours, and by the time you've bought two train fares, you'll be better of with a rental car. The drive from Berlin should be around two hours.