Complex sentence: Had the castle been built, it would have been located near Pfronten in southern Germany (not far from Neuschwanstein), and it would have been the highest castle in Germany at 1,268 meters above sea-level.
Split into simpler sentences: Had the castle been built, it would have been located at, near the town of Pfronten in southern Germany. It would have been the highest castle in Germany at 1,268 meters above sea-level.