It may be a bit touristy, but the Bruckenkeller Restaurant in Frankfurt had wonderful atmosphere [and maybe still does]. A cellar near a bridge, [naturlich], it has autographs from the crew of the Zeppelin Hindenberg as well as Swedish artifacts from the middle ages. A friend said one night there, "you can almost hear the bombs falling." I loved the saurebraten. For a cheap night, try the Sachsenhausen area with its apfelsaft bars and brats.