We will be doing a road trip starting from Frankfurt, head south, via Munich then east to Salzburg, then circle back to Frankfurt to fly out. We will have 15 days total. Now, we want to decide if we have time to circle back with these 4 places or must drop a couple as it may not worth the time.
Between these 4 places, let's say if we would NEVER be back in this area ever, what are the 2 places that we must visit?