There are an handful of train routes that will get you to Munich by day or by night. The simplest routes are via Paris from where you can board a high-speed service during the day or a sleeper train at night that will get you to Munich by early morning the next day. If you're headed from Brussels, head first to Frankfurt or Cologne from which you'll find numerous departures by train to Munich. Besides being a stepping stone to the rest of Germany, Munich has excellent connections to Switzerland, Italy and Austria beyond the Alps.