Queen Elizabeth II: Britain's Longest-Reigning Monarch

From Scandinavia, the Vikings emerged as a ruthless force, striking vulnerable targets with unmatched brutality and becoming some of the most feared warriors of the Middle Ages.

In 1953 Moscow, Joseph Stalin grows increasingly concerned about America's expanding nuclear arsenal, pushing to conceal a fleet of submarines worth billions inside a secret, nuclear-proof underground stronghold with a hidden gate.

From Renaissance-era predictors like Nostradamus, who wrote of the death of kings and the rise of evil, to 20th-century mystics like Rasputin, who foresaw the fall of a dynasty, were some predictions more than lucky guesses?

Most of the world's holiest places sit in plain sight, able to be seen and experienced. But there are some hidden deep underground.