The main rail route through the Black Forest runs north-south, following the Rhine Valley from Karlsruhe to Basel. There are fast and frequent trains to Freiburg and Baden-Baden from most major German cities (you generally have to change at Karlsruhe).
Local lines connect most of the smaller towns. Two east-west routes -- the Schwarzwaldbahn (Black Forest Railway) and the Höllental Railway -- are among the most spectacular in the country. Details are available from Deutsche Bahn.
Deutsche Bahn (0800/150-7090. www.bahn.de).