Salzburg is a lovely place. The obvious is to visit the fortress which a must see. You can hire an iPod type device for an audio tour. It's only a few Euros and is well worth the money, not like the boring, rip-off tours you get at other places - it's interesting and informative. The view from the top of the fortress is very impressive and unobstructed from a 'togging point of view.
If you have a car then I would recommend popping over the border to Berchtesgaden. You can visit the Kehlsteinhaus which will offer you the most spectacular views you are ever likely to see. I've been there and it's incredible, both as a viewpoint and a feat of engineering. You will need to check with the tourist office in Berchtesgaden first though as the house closes in early/mid Autumn dependant on the weather. It's also not worth paying the entrance fee if the cloud base is low as you won't see a thing, (and you will get wet!)
Enjoy Austria, it's wonderful. Don't forget you ticket for driving on the motorways though. Hefty fines if you don't have one and the police hang around the borders and airports waiting to nick unsuspecting tourists!