We have just a day plus 1/2 in Salzburg. I am drawn to the Sound of Music Tour idea (although I know it will be a little cheesy).
Suggestions of must see/do in that limited time.

Salzburg is such a nice town to walk around tho it can be quite crowded. We too have done the SOM tour several years ago and yes, it's cheesy but we had a blast.

Explore the castle on top of the hill, visit the old town including the Mozart house, check out several of the gorgeous churches and visit the Mirabell Palace and Gardens on the other side of the river. There is plenty to occupy you in the town for a full day. Also look into dinner at the stiffkeller (sp?).

Can you not see the mountains on the 2nd day on the way to wherever?

you can walk through the gardens of the Mirabell Palace, (Sound of Music site), visit the house where Mozart lived with his parents and sister there are exhibits of instruments he owned and other items if you want to do that; then cross over on the pedestrian bridge to the older part of town; Salzburg Cathedral is free, you can make a donation on your exit or not, its up to you. You can take the tram up to Hohensalzburg Castle where you will get a fantastic view of Salzburg and the mountains; down below you can walk around the old town area, there are a lot of shops and restaurants, Mozart's birthplace is also a museum.

The SOM tour will go to several places outside of Salzburg, so you will get an opportunity to see some of the lakes. I didn't do the tour, but did do touring of the lakes, and its very scenic.

Agree with much of the above: walking the old town is very nice, the castle is terrific (consider eating lunch and enjoying the view) and the churches are worth a visit. You probably don't have time but the other typical excursion options are the Eagles Nest and the Salt Mines. Have fun- it's a great city.

wunderbar2 did you take the bigf bus tour or the tours in the mini vans?