Lascaux Caves – France
Discovered in 1940 by four French teens and their dog, these prehistoric caves are some of the finest examples of cave art ever found. Although they were open to the public, they were closed in 1963 due to humidity and carbon dioxide damage, released by dozens of visitors each day.
Thankfully, the French government has recreated the cave (pictured above) down to the last detail, at a total cost of $64 million. Only scientists can see the real paintings, which are over 20,000 years old.