A century ago an epidemic put its victims to sleep, then locked the survivors inside frozen bodies for years. Doctors never found what caused it.

On a June night in 1912, an entire household in a small Iowa town was killed while sleeping. More than a century, two trials and countless theories later, no one has ever been convicted.

In 1994, nurses and doctors at a California hospital collapsed one after another while treating a dying woman. Three decades later, science still cannot fully explain what happened that night.

An 1885 pamphlet claimed a fortune in gold lies buried in Virginia, its location locked in unsolved ciphers. Skeptics say the treasure never existed — yet people are still digging.

In 1897, Edward Elgar slipped a note of curling symbols to a young friend. She never managed to read it — and neither has anyone else since.

In September 1944, an Illinois town armed itself against a prowler spraying sweet-smelling gas through bedroom windows. Police never found him — because he may never have existed.

For decades, silent balls of light have floated over a remote Norwegian valley — and for over forty years, scientists with cameras, radar and magnetometers have been trying to explain them. They still can't.

Every October, glowing orbs rise silently from the Mekong before enormous crowds. After decades of theories — from tracer rounds to swamp gas — no one has proven what they are.

Deep in the Siberian taiga, a geologist stumbled on a 40-meter mound of shattered limestone that seemed to have burst up from below. Seventy-five years later, science still cannot say for certain what made it.

A humble clay pot with a copper cylinder and an iron rod has been called the world's oldest battery. But the case for ancient electricity is thinner than it looks.