Eagle's Nest tickets in advance?

We were just there two weeks ago. The only ticket required to see the Eagle's Nest is for the special equipped bus that takes you up the mountain (bus #849) and that can be purchased on the day. Once you're up on the mountain, there is no entry fee to the Eagle's Nest. The starting point is just outside the Obersalzburg Documentation Center. We took a series of buses from Salzburg to get there, but I recall seeing a big parking lot so you should be able to drive to this point, park your car, and then buy your ticket for the #849 bus. We arrived around 10:30am, just before the rush and had no wait walking up to buy a ticket. We found that it was busier as we were leaving early afternoon, so your mileage may vary.

This is all assuming, of course, that you plan on doing this yourself. If you're actually planning on booking a tour, I can't comment as much about that as we didn't take one. Although, I can say that the tour Rick recommends in his book (David and Christine Harper) I actually inquired about before we left for our trip and they informed me they no longer do guided visits with a per-person price (as mentioned in Rick's book) -- only private tours. We found the price for the private tour was a little out of our budget so we opted to just do it ourselves.

This is great info, thank you!