A serial killer taunted San Francisco with encrypted letters. Two of his four ciphers have been cracked — one took 51 years — yet his identity remains a blank.

For over four decades, a shortwave frequency has broadcast a monotonous buzz from Russia, day and night. Occasionally a voice cuts in, reads coded names and numbers — and vanishes. No one has ever officially explained why.

In 1922, six people were killed on a remote Bavarian farm — days after the farmer found footprints in the snow leading to his house but never away from it. A century later, Germany's most haunting cold case is still open in all but name.

In 1977, a radio telescope in Ohio caught a powerful narrowband signal from deep space. It lasted 72 seconds, looked exactly like an interstellar broadcast should — and it has never been heard again.

In 1908, a blast many times more powerful than the Hiroshima bomb flattened some 80 million trees across a swath of Siberia larger than a major city. It left no crater, no confirmed fragment, and a question science still cannot fully close: what came out of the sky that morning?

Since 1795, treasure hunters have poured fortunes — and six lives — into one hole in the ground off Nova Scotia. Nothing conclusive has ever come out of it.

A 15th-century codex filled with impossible plants, bathing women and a script no one has ever decoded has defeated medieval scholars, WWII codebreakers and modern artificial intelligence alike.

A diver surfaced screaming about a heap of corpses on the seabed; they were bronze statues - and beside them lay a 2,000-year-old geared computer. New research keeps making it stranger: it tracked the lunar year with uncanny precision, yet its gears may have jammed when cranked.

In 1590, John White returned to Roanoke Island to find 115 colonists gone — and a single word carved into a post. Modern archaeology may finally be closing in on where they went.

In July 1518 one woman began to dance in a Strasbourg street. Within a month hundreds had joined her, and the city's official cure was to hire musicians. Five centuries later, no one can say what really happened.

He walked out of nothing into a Nuremberg square, claiming a lifetime in a dark cell. Five years later a stranger's knife — or his own — killed him. Two centuries and a 2024 DNA test later, we know who he was not, and still not who he was.

Abandoned in the Arctic ice in 1931, the crewless SS Baychimo went on sailing by herself for nearly four decades - sighted, boarded, stripped of furniture and a whaleboat, and lost again, until she vanished for good.