Nesting falcons, mating toads and other wildlife take over the 500-year-old Heidelberg Castle in Germany.

The ancient stone fortress of Carcassonne in France has transformed into a sanctuary for avocets, flamingos and other birds.

Brown bears and aquatic salamanders find sanctuary in Slovenia's Predjama Castle and its eerie caves.

Iberian frogs, white-bellied hedgehogs and other wild creatures reside in Southern Spain's Alhambra palace.

Despite being one of Germany's most-visited attractions, Neuschwanstein castle and its surrounding forests also hold importance for a variety of creatures and has been a natural haven for centuries.