There are a lot of things in the world that we don't quite understand. And there are some things that we'd probably be better off not knowing about.
Case in point, a 400ft-deep hole in the sea.
With most of the world's oceans being unexplored by humans, it's no wonder it gives some of us the heebie-jeebies.
The Great Blue Hole is located 60 miles off the coast of Belize.
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The rim rises up out of the Caribbean Sea, so it's not hard to miss either.
This hole was made famous by French explorer and naval officer Jacques Cousteau.
Cousteau was a groundbreaker in the field of oceanography, being the co-inventor of the self-contained underwater breathing apparatus (SCUBA). He also produced some of the world's first underwater documentaries and wrote books on his incredible findings.
Cousteau's grandson Fabien would continue his grandfather's legacy by journeying down the giant hole in 2018.
He made this journey alongside Richard Branson, travelling in two submarines.
As you might imagine, a 400ft pit isn't the most welcoming and hospitable place. At around 300ft, they discovered a layer of hydrogen sulfide.
Below that point, the water was dark and devoid of life. But there was more to come.
When the explorers finally made it to the bottom, they made a disturbing discovery.
There was some rubbish lying on the ground, including a two-litre plastic bottle, as well as a long-lost GoPro.
The GoPro contained some shots from a holiday. Usually seeing someone's vacation snaps would be enough to inspire envy, but in this situation, it'd be enough to send a shiver down your spine.
However, that's nothing compared to the two bodies also sitting down there.
These were explorers who had gone missing on a previous expedition.
While the living explorers determined it'd be best to leave the corpses put, they did inform the Belize government. The hole was also filled with a series of caves, filled with hanging stalactites - mineral formations found on the ceilings of caves.
Visualise a stone icicle and you'll have a clearer idea of what they look like.
At any rate, they form in caves above water level so seeing them down below was rather unusual.
This indicated that this hole had once been on dry land.
Writing on the Virgin website, Branson reflected: "The Blue Hole is made of a complex system of caves that once formed on dry land. It is proof of how oceans can rise quickly and catastrophically.
"Sea levels were once hundreds of feet lower. 10,000 years ago the sea level rose by about 300 feet when a lot of ice melted around the world. At 300 feet down you could see the change in the rock where it used to be land and turned into sea."
He said it was 'one of the starkest reminders of the danger of climate change [he's] ever seen'.
Topics: Science, Richard Branson, World News
Ben Thompson