Untersberg is a must see when you are in Salzburg. There is a cable car that takes you to the top which is around 1800 meters . We were there in the second wk of this month and there was snow on the top. The view is excellent from the top snd you can see Salzburg from there.
The cable car would cost 21 eur for round trip however it is better to buy Sakzburg card which has free entry to al attractions in the city.