It is the Hohensalzburg Castle. It sits over the city. The pictures I took looking down on the city were taken from the castle.
Here is a bit of history:
Constructed originally in 1077, but was expanded over the years with the ring towers and walls being built in 1462. The rail way that goes to the top was originally built in a very primitive form in 1495. It is the oldest continually used rail service in the world. It was used a prisoner of war camp during WW1, housing Italian POW's.