Salzburg was Mozart's birthplace and the setting of the Sound of Music, on top of which the old town was listed as a UNESCO World Heritage Site in 1997. So it has a bit of tourist value going for it. They still offer Sound of Music tours.
A textbook example of 17th century Baroque construction, Salzburg Cathedral has ceilings that would make Michelangelo blush. The four organs ringing the transepts create some serious surround sound.
A tourist attraction since 1892, Hohensalzburg Fortress is one of the largest and best-preserved castles in Europe. Founded in 1077, this hilltop castle has undergone various permutations and expansions over the centuries, but only saw combat once: during the German Peasants' War in 1525, when a group of miners, farmers and townspeople tried to storm the walls and, not surprisingly, failed.
Contrasting with the opulence of Salzburg Cathedral, Franziskanerkirche (the Franciscan Church) is a brilliant Gothic structure: dark and eerie, with vast and empty high spaces. Someone tried to cutesy it up by filling the naves around the altar with Baroque cherubs, but they just look like cardboard-box dioramas dropped into a dark alley.