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

The introduction of the scientific method transformed society by using science and reason rather than political or religious dogma.

Beneath the streets of Paris, France, are the bones of more than 6 million people in what's known as the Paris Catacombs.

Queen Elizabeth II, the longest-reigning modern monarch in British history, redefined what it meant to be a monarch and navigated a tremendous amount of change within her family, country and world.