Mines or Eagle Nest?

The Eagles' Nest. There are lots of salt mines, but only one Eagles' Nest.

I would say it is weather dependent. If you can make the weather decision then: Bad weather mines, good weather outside. I am not familiar with the Wieliczka Salt Mine. You could be in hours long lines waiting for the trip to the Kehlsteinhaus. If the weather is bad I would skip it. Maybe a trip to Berchtesgaden? Where are you basing and what are your options?

I understand that you may only have these two tour options but... Good weather I would recommend the electric boat am Königssee und St. Bartholomä over the Kehlsteinhaus, even if you are a history buff. Nice views from the Kehlsteinhaus, but Königssee is part of the Nationalpark Berchtesgaden. The boat tour gives you great views, trumpet echo yodel and options to go to the Obersee, This would be an all day thing.

I'm with Lee on this. Definitely the Eagle's Nest.

The Eagle's Nest tour was very good -- historical and awesome views -- but then due to slight claustrophobia I avoid mines!

Depends on what you are most interested in...WW2 history and spectacular views over the alps OR an adventure sliding down into the mines and walking through, learning about their history. Both are fantastic just in different ways.
I don't know if it helps but you can do both in one day. We toured the salt mines in the morning and visited the Eagles Nest in the afternoon. I would recommend making reservations at the mines ahead of time to make sure you don't have to wait around too long. It can be very busy certain times of the year.

jean,

The Eagle's Nest is mostly about the history and the views. When is this trip taking place? If the weather is bad, you won't be getting good views from the Eagle's Nest. Also if you're travelling too early or too late in the season, the road to the Eagle's Nest may not be open yet. You could also visit the Dokumentation Centre & Bunkers which is just above Berchtesgaden.

As someone else suggested, you could always tour the Salt Mines in the morning and the Eagle's Nest in the afternoon. There are also historic Salt Mines in Hallstatt, should you be travelling in that area. I haven't been to the Salt Mines in Krakow yet, but based on what I've seen on Rick's TV shows, those are larger and contain large chapels, salt chandeliers and other facilities. The mines in Berchtesgaden and Hallstatt are not that elaborate, and give more of an impression of a working salt mine.

We are on a coach tour and stopping in Saltzburg the middle of October; is this too late in the season to get a clear day? The tour is offered as an add on so it'll be open to tour...

jean,

It's difficult to predict whether a visit to the Eagle's Nest will be possible in mid-October. I believe the site is normally closed from about November 1st to May, but if that area gets an early snowfall the road up to the Eagle's Nest will be closed. You might just have to "take your chances" on the Eagle's Nest, but have a backup plan.