Chernobyl is a city in the Ukraine located about 56 miles (90 kilometers) northeast of the capital, Kiev.
Prior to the disaster and a subsequent evacuation, it was home to around 14,000 people.
At that time, it was still part of the Soviet Union.
The city was the location of the first ever nuclear power station to be built in Ukraine, but on the 26th of April, 1986, disaster struck when Reactor No. 4 exploded.
The town is still home to around 690 people, although it's now somewhat of a ghost town, with animals occupying many abandoned buildings.
Most of the residents live about 19 miles (30km) from the disaster site in the Chernobyl Exclusion Zone, and surprisingly, international tourists flock to the area.
But what exactly happened in Chernobyl?
That's what we'll find out today, in this episode of the Infographics Show, What Caused the Catastrophic Nuclear Accident in Chernobyl?
As CNN reported in 2016, if you visit Chernobyl now as a tourist, you'll be taken on a strict guided tour of what was once a busy, if not small, city.
Photographs show a place that has been frozen and overgrown, a kind of spooky remnant of a town where people once lived and worked, and where kids played on the now unused ferris wheel.
The explosion at the nuclear plant is rated as the worst nuclear disaster in the history of the world.
Radioactive dust was sent far and wide, transported by winds as far as Sweden.
The number of deaths directly related to the initial explosion is thought to be about 31, although the WHO reports that a further 50 deaths happened later, as a result of massive exposure of radiation on the day.
These deaths were mostly workers and rescue workers.
Two people died as a result of injuries suffered because of the blast of the explosion.
The WHO further states that around 4,000 deaths in total can be attributed to radiation exposure, because of the event.
On the day of the disaster, thousands of people were exposed to high levels of radiation, with the WHO saying these people are at high risk of having cancer in their lifetime.
Even the millions of people that lived miles away from the site in other parts of the then Soviet Union, were exposed to low levels of radionuclides ( or atoms that contain excess nuclear energy), and they too are more at risk, regarding cancer.
On top of that, many of those displaced suffered financially and psychologically, especially because some were never given sufficient information, regarding the danger they had been exposed to.
According to recent reports, areas at least 19 miles (30 km) away from the accident site, are mostly radiation free, although some lakes and forestland are no-go areas or are at least restricted to the public.
"In most areas the problems are economic and psychological, not health or environmental," said Dr. Mikhail Balonov, a radiation expert and the scientific secretary of the Chernobyl Forum.
So yes, this is now a tourist spot for those who want to see what a ghost town looks like.
We looked at blogs written by travelers who have visited the exclusion zone.
One of them wrote that when she was invited, she thought it was a joke, thinking like many people that visiting such a place was too dangerous.
She wrote that in the absence of people, the area has once again become home, to wandering bears, wild horse, deer, foxes, wolves… and dogs, lots of stray dogs.
While you are told not to touch things, or eat or drink while on the tour, the radiation levels are checked by your guide throughout the visit.
"I felt like I was walking through a horror themed park,"she said of an abandoned kindergarten, saying dolls were still hanging around.
Anyway, you get the picture, let's now talk about what happened on that fateful day.
Ok, so according to the World Nuclear Association, this is how it went down.
We will try and explain it as clearly as we can, because it's not all that simple if you don't work as a nuclear power engineer.
The workers at Chernobyl reactor 4 were performing a test, to see if the turbines could provide enough energy to keep the coolant pumps running if there was a loss of power, and if they could keep them running until the emergency diesel generator kicked in.
They'd done this test before, but the tests had been unsuccessful.
They turned down the reactor to 25 percent of its capacity, but a problem arose when the power plummeted to one percent.
They then tried to increase the power, but what ensued was a massive power surge.
The reactor's emergency shutdown failed.
One engineer had wanted to abort the test but was told by a senior to carry on.
The reactor then became even more unstable.
This caused considerable pressure, and according to one step-by-step report one engineer witnessed, "the 1.5 ton (350 kg) blocks atop the fuel channels of the Upper Biological Shield began jumping up and down, and you could feel the shock waves through the building structure".
What did he do then?
Of course, he ran for it, down a series of steps to report what he had seen to others.
The pumps failed, there was no water flow, and the reactor started to make loud noises.
As another website tells us about the sudden increase in power, "A peculiarity of the design of the control rods caused a dramatic power surge as they were inserted into the reactor".
Hot fuel combined with cool water, created a mass of steam that couldn't escape and caused lots of pressure.
This lifted a 1,000-ton lid and here we have the start of the radiation leak.
Air got into the reactor and caused a graphite fire.
A second explosion happened when hydrogen was formed by hot water steam contacting zirconium.
This was a much bigger explosion than the first, and it threw debris everywhere.
Power went out, except for battery-powered lighting.
The air was filled with dust.
One man died, and his body was encased in all the debris.
Burning fuel started fires everywhere and radiation was cast into the atmosphere.
All the internal phone lines went down, and workers fled from the scene.
Firefighters arrived, apparently unaware of the danger they were in due to the radiation leak.
One even joked about it, saying, "There must be an incredible amount of radiation here, We'll be lucky if we're all still alive in the morning".
He was kidding, but he wasn't far off.
As one woman explained, the next day she found out there had been a fire, but the kids still played, they went to school, people still milled around in the street, even though she said, "All the roads were covered in water and some white liquid. Everything was white, foamy".
She added that she wasn't told about the danger of radiation, stating,"About radiation, that radioactivity was escaping, there was not a word".
The reactor was filled with water, but then flooding was a problem.
After that, for days, thousands of tons of clay, sand, boron, and dolomite, were dropped by helicopter into the burning reactor to quell the fire, but also to try and prevent the spread of radiation.
For 10 days, a large amount of radioactive substances pervaded the air, most of it falling as dust into nearby areas, but smaller particles spread far and wide carried by the wind.
We all know what happened next.
We should add that there are numerous scientific theories as to exactly what happened that day, and this is just a basic summary of the most widely held belief.
Hopefully, something like this never happens again.