Driving a rental car, probably you are coming into Old Town Salzburg thru the tunnel. Just as you emerge from the tunnel there is a traffic light. Turn left. Immediately on your right is the BLUE exterior of the Blaue Gans (blue goose) hotel. There is a back in car unloading spot for one, maximum 2 cars. Don’t miss this! You will be right outside the reception desk.
The nice folks there will tell you all about the relatively nearby paid parking.