5. Lascaux Caves, France

Although the Lascaux Caves in France are a UNESCO Heritage site, it is not open to the public. Since 1963, France banned the public from entering the caves due to fungal invasions that could be destructive to its preservation. But why are these caves so precious? They give insight into the history of the human species. 

The caves contain over 600 examples of prehistoric art that date back about 20,000 years. Although people can't go inside the real caves, it is possible to experience them in the museum and replica built right next to the actual caves.