Predjama Castle, built in the 9th century in the Slovenian Karst Plateau, is characterized by a unique cave and tunnel system in the limestone mountains. Due to a geographic curiosity, the rivers here seem to flow upward. Where the source of a river should normally be, the river flows directly into the mountain. Holes in the massive mountain eject water that runs back into the cliffs further down. Peregrine falcons, once endangered in this region due to hunting, have now returned and observe Predjama's mystic scenery.