How to Get There
By train to Berchtesgaden Hbf, then RVO Bus 838 to Eagle's Nest bus stop. After that, a separate RVO 849 (not covered by Bayern Ticket) takes you to Eagle's Nest.
This is near Salzburg and might make sense as a combined trip.
About
Eagle's Nest was Hitler's home atop the alps, and currently is a museum to WWII and restaurant with stunning views.
This webpage has helpful information about visiting.
The official website is also useful.
The town of Berchtesgaden provides 360 degree views of the Alps and a palace dating to the 1100s. It is the gateway to Eagle's Nest.