Getting Around in Berchtesgaden National Park

If you are going all the way to Berchtesgaden, plan to also include Eagle’s Nest, Hitler’s escape to cottage on top of the mountain, glorious views.

https://www.nationalpark-berchtesgaden.bayern.de/english/service/getting_there/bus_train/index.htm

I've spent all or part of 13 days (8 nights) in Berchtesgaden in the last 25 years, and I've never needed a car, neither to get there nor to get around there.
To get there from the Munich airport, use a Bayern-Ticket and take the S8 (every 20 minutes) to the Ostbahnhof, then an hourly regional train to Freilassing (destination Salzburg), where you transfer to a local train to the Berchtesgaden Hbf.
I've always stayed down below the town, near the Hbf. There are buses from the Central Bus Station at the Hbf to just about every place in the area you want to go to. In my times there, I've visited the Eagles' Nest, Dokumentation Zentrum, Königssee, Wimbachklamm, and the town of Berchtesgaden, all by bus. The place I stayed at the last three times gave me a pass for the buses in Berchtesgaden (except the special bus to the Eagles' Nest). I've never gone to the salt mine, the spa, Ramsau or the Jennerbahn but all are easily accessible by bus. The same bus that goes to Königssee stops at the Jennerbahn valley station; the same bus to Ramsau stops at the trail to Wimbachklamm.

Although I always had a car when staying in Berchtesgaden you easily can go by bus to the most locations where you can start hiking

a special option for an easy walk is the Almerlebnis-Bus starting from the Nationalpark House (stop Auzinger)next to Hintersee lake near Ramsau

Go with the bus up to the Alpengasthof Hirschbichl in Austria and walk all the way down through the Klausbachtal Valley back to the Nationalpark House Info Center seeing Bindalm Huts on the way (total distance 7km)

With your guest card from your accomodation you can use almost all buses in the region but you have to pay extra for the above mentioned Almerlebnis Bus
So go free from your location to Hintersee Nationalpark Info Center and take the Almerlebnis Bus from there at an extra cost.
Its worth it (8Euros as far as I remember)
We parked our car at the Info Center Car Park and took the bus up to Hirschbichl and walked from there
The road is only open to the bus and no other public traffic