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Scientists have discovered a mysterious nine metre long chamber inside the Great Pyramid in Egypt.

There are more than 100 surviving pyramids, but the Great Pyramid is thought to be the largest standing at more than 146m high.

The spooky corridor was first unearthed back in 2016 but it has only recently been seen using high-tech equipment.

The tunnel is 2.1m wide and was first found using an advanced search technique called muography.

Muography is a specialist procedure that doesn't disturb the 4,500-year-old pyramid's structure.

Muons are subatomic particles that can't pass through stone. A team from a project called ScanPyramids fired the particles into the pyramid where specialist cameras could analyse their movement safely from the outside.

This found there was a void or space that they had never known existed before and can't be accessed by a person from the outside.

Once they had done more tests to make sure it was safe, they sent a tiny camera, called an endoscope, through a small gap in the stone near the main entrance.

The camera itself was just six millimetres wide but it was enough to confirm the existence of the chamber and wow the researchers.

The discovery was presented to the press at a news conference where they showed the video footage from inside the chamber.

It showed an empty corridor-like space with walls made out of stone blocks and a triangular vaulted ceiling.

Mostafa Waziri, who is the head of Egypt's Supreme Council of Antiquities, said they thought the cavern might have been created to balance out the pyramid's weight around the main entrance or another as yet undiscovered chamber.

"We're going to continue our scanning so we will see what we can do... to figure out what we can find out beneath it, or just by the end of this corridor," said Waziri.

The baffling chamber could be key in unlocking the thousands of years of questions these pyramids hold.

Although archaeologists have been studying them for years, nobody can agree how these massive structures were built using ancient technology and building techniques, and how they are still standing impressively to this day.

It's not the first time a space has been discovered inside the Pyramid. Another huge void was discovered back in 2017, where it was thought to be big enough to fit a 200-seat passenger plane!