The "Hobbits of Flores". The local people had an oral tradition of stories about these little people. It was considered to be a myth or a legend, until the bones were found.

Interestingly, the locals have stories of the hobbits up until the 19th century. Presumably these later stories are myths, because we never found bones that recent. But what if...

For a long time, the only knowledge to the Hittite civilization was their reference in the Hebrew Bible. Turns out they were a pretty big deal in what is now Turkey.

Kangaroos were once classified as Cryptids (along with Bigfoot, Loch Ness monster, etc.)

Before it was established that they kept their babies in their pouches, it was told that they were "creatures with two heads". Makes me think what other cryptids we actually are just seeing wrong.

Ball lightning is pretty fascinating.

There have been anecdotal reports of it for hundreds of years, but it was hard to document because it doesn't last long and it couldn't be photographed. It's also hard to create it in a lab. But it is acknowledged now that it does exist.

I first read about it in one of the Little House on the Prairie books and thought it was wild. I wasn't sure if it was real or some kind of hallucination.

The Shang Dynasty, China's second dynasty according to traditional historiography.

Until the 20th Century, there was no direct evidence that it had existed besides records describing it left behind by dynasties that came centuries after them, and it was ascribed semi-mythical status.

Then one day somebody realized that "dragon bones" being ground up by a bunch of villagers to make medicines were actually oracle bones, the first direct written evidence of the Shang Dynasty's existence left by the dynasty itself.

The dynasty preceding the Shang, the Xia Dynasty, is still considered mythical, and since it precedes writing its existence is harder to verify.

Edit: Archeologists have however recently found evidence of a massive flood on the Yellow River 4000 years ago that has been suggested to correspond with the Great Flood of the Xia Dynasty's founding myth.

The coelcanth. It's a type of fish that was thought to be extinct for over a hundred million years, until it was found off of the coast of Madagascar in the 1930s by a fisherman. It's a pretty cool story – really makes you question what's out there.

The Japanese Divine Wind legend. Said to have saved the Japanese from two Mongol invasions and ultimately play a major role in the fall of the Mongol Empire.

Turns out it did happen, but the reason the Mongol's boats sank was because the Chinese ship builders intentionally built a fault into the ships that would cause them to sink once wind/sea conditions hit a specific level. The Mongols who knew nothing about ships were totally oblivious to the subtle built in error.

The Divine Mistake.

In the 1960s there were rumours that the US government had been carrying out secret germ-warfare tests on its own citizens. These rumours were strongly denied.

Then in the 1970s, when pressed by Senate hearings, the military admitted that, between 1949 and 1969, such tests HAD taken place, most notably on the New York subway system.

Troy was once thought of as a myth.

North Korean kidnappings of some Japanese people.

They were just rumors and a 'myth' for a while, but then NK came out and admitted that they totally did it.

Machu Picchu

" So you're telling me there are a bunch of people with a ton of gold living on the top of a mountain higher than any in Europe using advanced farming techniques and building magnificent​ temples? Nonsense"

Turns out, yes Mr. Conquistador, there was.

One of my favorites is Lake Nyos in the Republic of Cameroon.

The local legend was that an evil spirit or a monster lived in the lake and would come out at night to takes lives of anyone who lived too close to the lake. One of the local groups, the Bafmen, settled in the high ground near the lake due to the legends. Different groups moved into the area in the mid 1900's and lived closer to the water's edge, disregarding the customs of the Bafmen.

In 1986, nearly 1,500 people living near the lake were found deceased. Those who lived in the higher ground were fine.

It turns out the lake was very deep, and would essentially become carbonated. A land slide could trigger a release of CO2 from the lake waters. On that night in 1986, an enormous release occurred and since CO2 is heavier than air, anyone in the lower areas simply suffocated and didn't wake up.

So while the myth about the evil spirits wasn't entirey true, there really was something in the lake to fear!