Berchtesgaden as Munich Day Trip?

I usually encourage people to use the regional pass (Bayern-Ticket) when traveling in Bavaria, but to make a day trip to Berchtesgaden, I think you have to bite the bullet and pay full fare so you can leave early in the morning (unless on a weekend, when you can leave anytime). It's a fairly long trip to Berchtesgaden. I would really recommend you make it an overnight (several overnights) trip.

If you just want to visit an Alpine resort, Garmisch-Partenkirchen is much easier to reach as a daytrip from Munich. Even here, though, it would be preferable to stay a few days.

We have done this as a day trip from Munich and it made for a spectacular albeit full day. We took a very early morning train from Munich. The thing that made the trip was being lucky enough to book a tour with Eagle's Nest Tours.http://www.eagles-nest-tours.com/EN/eagles-nest-tours/index.php?navid=2
We were beyond lucky to be there on a clear day in June, and the quality of the information from Christine Harper who runs the company was only surpassed by the unforgettable views. This is a must do if you are going to Berchtesgaden.
We followed the instructions given in the RS Tour Germany tour book. His direction to get to Berchtesgaden are from Salzburg, but are easy enough to adapt if you are leaving from Munich as we did.

I agree that the view from the Kehlsteinhaus are great, but I am not an Eagles Nest fan. Tourist Mecca... For me time is better spent on an electric boat ride to and from St. Bartholomä on the Königssee in the Alpen Nationalpark Berchtesgaden. Also touristic, but not so many from USA, but still a lot of tourists. Great weather factors in here for either place. I would recommend at least an overnight in the area. This is a good place for dinner in Schönau am Königssee I can recommend http://www.gruensteinstueberl.de/Home and they have grill evenings in the Biergarten in Sommer. Maybe a stay in Schönau am Königssee is preferable to Berchtesgaden. You would have to take a bus to Schönau from the Berchtesgaden train station.

http://www.koenigssee.com/

http://www.seenschifffahrt.de/koenigssee/fahrplan/fahrplan-und-fahrbetrieb/

http://www.jennerbahn.de/de/home/

Do you need a formal tour to visit the Eagle's Nest? Or can you hike up on your own from Berchtesgaden? We will be in Salzburg in June and are considering a Berchtesgaden visit.

There is no one checking tickets for people going into the Eagles Nest building, itself, but they might ask for one if you wanted to go up the elevator. But then, if you had already hiked up from Obersalzberg, what would another few hundred feet up be. I remember on one trip up seeing people hiking up to the Nest from below.