Mozart's birthplace, a fortress you can see from everywhere, The Sound of Music locations, and arguably the best Schnitzel in the world. Just 1.5h drive from Munich.
Munich to Salzburg is one of the most scenic drives in Europe. Take the A8 autobahn south-east toward Salzburg. As you approach, the Alps start to appear. The Austrian border is seamless (Schengen zone — no passport check). Park near the Altstadt — there are multi-storey car parks on the edge of the old town.
Austrian vignette: Austria requires a motorway toll sticker (Vignette) for driving on motorways. The hire car should have one, but verify with the rental company.
Austrian motorways require a toll sticker (Vignette). If the hire car doesn't have one, you need to buy it at a service station near the border. A 10-day vignette is ~€9.90 and available at petrol stations. Driving without one risks a fine. Verify with the hire car company before departure.