Biking, easiest way to get around
Salzburg is perfect for biking around. There are plenty of places to rent a 3 or 21 speed bike. The likelihood of you staying by the train station or outside the main attractions is high.
Salzburg has paths along the river set up for biking. It's perfect to cover a lot of ground in a few hours. If you go up to the fortress, just park and lock your bike at the bottom. I walked one day, and biked the next. I wish I had biked both days. I even biked to the Augustiner brewery one night.
Must see the Old town with the...
Must see the Old town with the Salzburg Castle on top of the hill over looking old town. This is probably one of the most beautiful and interesting Castles in all of Europe. Walking around 'Old Town' under the watchful eye of the Salzburg Castle, and listening to all of the beautiful street Music, from the Ancient instruments to Gypsy type Music from Peru, to the most skilled violenist playing Mozart. It was Wonderful!
Salzburg in two days
I lived in Salzburg for four months and if I could live in one European city and speak the language proficiently, it would be Salzburg. (If anyone knows a job in Salzburg that needs only English-speaking employees, let me know.) However, based on my knowledge of the city and what tourists are interested in, I think it is safe to say a good two days is all you need to see the city well. One day you'll see a lot and can probably see most of the "must sees", but you won't get the full tourist package and you'll just leave the city wanting more.... which, unfortunately, is likely how you'll leave it no matter how many days, months or years you stay there. In two days, I would recommend spending between .5 and .7 days in new town walking around linzergasse and mirabell gardens and some of the other nice sidestreets. Also, you have a nice selection of restaurants on this side and a pension Trumer Stube which is excellent. Then, I would dedicate 1 full day to walking around old town, seeing residentzplataz, mozart platz, St. Peters, Getreidegasse (look at Mozart's birthplace, don't go inside though), the horse fountains, the road going through the mountain, the castle/fortress (only spend a half day or less at the top -- don't get carried away). Then, for the last .3 to .5 of a day, I'd choose one outskirt voyage... walking to Schloss Leopoldskron or a bus to Helbrun or a long walk along the river. Be sure to stop for short snacks (wurst or kebaps) and nice lunches and dinners (don't forget the applestrudel). One or one and a half days is just a tad too little. Three days is starting to get redundant with sites (unless you dive into museums and other inerds of the city). Two days should be perfect for a backpacker or tourist wanting to move on to Prague, Munich, Vienna, Venice or Zurich.
Every Thursday, even in winter a nice flower market is held on Residenzplatz in the New Town. I was quite surprised when I stumbled across this small, charming market right as I started my sightseeing tour at Schloss Mirabell.
It was somehow funny to see the blooming flowers and the snow on the ground next to them on a crisp and sunny winter morning.
Mozart balls, Mozart balls,...
Mozart balls, Mozart balls, everywhere Mozart balls! Little foil-wrapped chocolate balls with marizpan and nuts inside: delicious! But which one's the best? In my humble opinion, the Mirabell Mozartkugeln (not pictured here) are the yummiest. They are completely round (not with the flat bottom) in the gold foil. They clearly say 'Mirabell' on them. But try them all and see which one you like best!