Berchtesgaden station has very good connections via the InterCity train "Königssee" from Hamburg via Hanover-Würzburg-Munich-Berchtesgaden. With a change in Freilassing, there is also the InterCity or EuroCity from Frankfurt to Salzburg via Heidelberg-Stuttgart-Munich. In addition, regional trains run on the Berchtesgaden-Munich route, changing trains in Freilassing. From Freilassing to Berchtesgaden, the Berchtesgadener Land Bahn (BLB) operates.
By the way: According to the DB initiative "Fahrtziel Natur", the Berchtesgaden National Park is one of the most beautiful nature destinations in Germany, Austria and Switzerland!
On site, the RVO (Regionalverkehr Oberbayern) will take you by bus to the various entrances to the national park. For holders of the guest card of the valley basin communities, the use of the buses on site is free of charge!