Falkenstein Castle or Castrum Pfronten is a High Middle Ages castle ruin in the Bavarian Alps, near Pfronten, a town in southern Germany. The ruin's German name is Burg Falkenstein ("Castle Falcon Stone"). At 1,268 meters above sea level, it is Germany's most elevated castle ruin.
King Ludwig II of Bavaria purchased the ruin in 1883 and planned to transform the site into a magnificent fairy tale schloss (formerly schloß). However, the plans were abandoned upon his death in 1886.