A three-metre slab covered in an unknown script stood at the mouth of the Singapore River for centuries. In 1843 an engineer blew it up to widen the harbour. One fragment survives, and the writing has never been deciphered.

On a Sunday morning in 1942 a US Navy blimp drifted out of the fog and settled onto a California street. The radio worked, the parachutes were stowed, the doors stood open. The two officers who had flown it were gone, and they have never been found.

A crater in the Turkmen desert has been burning for around fifty years, and millions of people know exactly how it started. The problem is that the story does not appear in a single document, and the geologists who worked there tell it differently.

On a clear winter morning in 1909 a brand new liner overtook a cargo steamer off the coast of South Africa, exchanged polite signals, and pulled ahead. Nobody has seen her since, and after a century of searching not one plank has ever been recovered.

A civilization of a million people left behind planned cities, covered drains, standard weights and about four thousand tiny inscriptions. After a century of work nobody can read one, and some scholars argue it was never writing at all.

For sixty years the skeletons in a frozen Himalayan pool were explained by one storm and one doomed pilgrimage. Then a genetics laboratory read their DNA and found three different groups, a thousand years apart.

On a Sunday night in 1987, a grinning rubber mask seized two Chicago television stations and spoke gibberish to a city. Federal investigators had every advantage and never came close. Nearly forty years on, not one person has been identified.

Federal and state agents searched his Georgia clinic on 16 June 2015. Three days later the autism physician was found dead in a North Carolina river, and the sheriff ruled it a suicide. His family never accepted that, and a much larger conspiracy story grew out of the case, one that investigators and fact checkers later took apart.

In August 1991 NOAA tapped into the US Navy's undersea listening network and found a signal nobody could name. It has repeated ever since, peaking every spring and autumn, from an empty patch of the South Pacific. It is fading, and no ship has ever gone to look.

Diaa al-Awady told millions of followers that food could replace medicine. Egypt revoked his licence and closed his clinics. In April 2026 he was found dead in a Dubai hotel room, and the official answer that followed convinced almost none of the people who had believed in him.

For more than a hundred years, farmers, colonial surveyors and trained field biologists have described the same small upright ape in the forests of Sumatra. There are footprint casts, hair samples and a fifteen-year camera-trap project. There is still not one photograph, and not one bone.

Between 1764 and 1767, something hunted people in the highlands of south-central France. It killed around a hundred of them, most of them women and children. A king sent his own hunters, two animals were shot and paraded as the culprit, and no one ever proved what it was.

For more than a hundred years, expeditions have pushed into the flooded forests of the Congo Basin after a large unknown animal. They came back with recordings, blurred film and hundreds of interviews. They never came back with the animal, and the dinosaur story attached to it may not have started in Africa at all.

A Hungarian count gave away his library in 1838. Inside it sat a small, fat book written in a script that matches no alphabet on earth. Nearly two centuries and a dozen rival decipherments later, not one sentence of it has been read in a way other scholars accept.

A hotel maid found the greatest electrical inventor of the age dead and penniless in a small Manhattan room. Within two days federal agents had hauled his papers away in trucks. What they took, what they returned, and what never reached Belgrade is still argued about today.

In the 1930s, bulldozers clearing jungle for banana plantations in southern Costa Rica began turning up giant stone balls, some taller than a person and weighing as much as a loaded truck. Workers dynamited many of them looking for gold inside. Nearly a century later, nobody can say for certain how they were carved so precisely, or what they were for.

At eleven on a Sunday morning in 1978, something detonated over a small iron-mining island in Newfoundland. Fuse boxes threw blue flame across rooms, televisions burst, a shed came off its foundation with the chickens inside, and two neat holes were punched into a field. American satellites built to catch nuclear tests registered the flash, and Los Alamos sent scientists. Nearly fifty years later the file is still open.

More than a hundred hollow bronze dodecahedra have been dug up across the northern Roman provinces, each pierced by holes of different sizes. Not one Roman text, inscription or image mentions them. In 2023 a field in Lincolnshire produced the finest example yet, and the mystery only deepened.

On a Victorian bridge outside Dumbarton, dogs have been going over the same few metres of parapet for seventy years, almost always on clear days, almost always long-nosed breeds. In 2005 two specialists went looking at the bridge through a dog's eyes and came back with an answer involving a smell no human can detect. The answer still has holes in it.

For more than a hundred years, travellers crossing outback Queensland have described a light that rises out of the dark, hovers above the horizon, and follows them for kilometres. In 1992 a neuroscientist built one to order, using nothing but a car and ten kilometres of empty road. Boulia was not entirely grateful.

For generations the villagers of Shiyan Beicun believed their ponds were bottomless. In 1992 four of them bought pumps to find out, and drained the water off the roof of a hand-carved hall the size of a church. Twenty-four of them have now been opened, and not one line of Chinese history mentions that they exist.

Across the highlands of northern Laos stand thousands of carved stone jars, some weighing fourteen tonnes. A French archaeologist called them tombs in the 1930s. Then the bombs fell, and it took eighty years to get back to the question.