Trains are about 10 hours for Bremen or Hamburg.

Oh ah looking a bit harder : Lyon to Hamburg looks perfectly feasible : TGV to Basel then sleeper! Competitive with flying, probably cheaper counting accommodation, and saves faffing around after an evening flight, or the indignity of sleeping on airport benches (not that it's beneath my dignity)
Lyon to Bremen is feasible too, though with two stops.

Copenhagen's out of reach by rail (sleeper, via Hamburg or Cologne, but nearly 24h overall). I'm happy to spend a night on the train, but not to lose a day each way.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}