I will briefly give my opinion on the possible hidden rooms under the pyramids and the sphinx.
Rumors about hidden underground rooms under the sphinx and pyramids appeared long ago. Many believe that somewhere in the underground vaults of Egypt may be hidden secret knowledge of the Atlanteans or other advanced ancient civilizations.
At the moment, I have not met any worthy factual confirmation of these rumors, but I have not met any facts refuting this version.
Although, if I'm not mistaken, somewhere in the ancient texts it was said about a certain underground library under the pyramids. However, it also said about the construction of the Cheops pyramid in 20 years, which means it should not be taken as a fact. But there is one interesting circumstance that makes us think about this version in more detail.
In 1989, a group of Japanese scientists conducted special studies under the sphinx and some pyramids in order to identify underground voids. The most amazing thing is that the equipment showed their presence!
But after a surprising discovery, the Egyptian authorities promptly curtailed the group and expelled it from Egypt. At the same time, the research remained either incomplete or later classified. And this is already a fact that deserves attention.
In the same 1989, similar studies were conducted by the American researcher Thomas Dobecki. His findings coincided with those of his Japanese colleagues. Is this a mystical coincidence?
After 4 years, the Egyptian authorities completely banned the study of the sphinx and pyramids without special permission. But they stopped issuing permission under various pretexts.
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Based on the facts described above, one can make the assumption that something is hidden under the Egyptian pyramids and the Sphinx. The Egyptian authorities are probably aware of what is at stake, but do not want to bring the information to public comment. I wouldn't even be surprised if they secretly explored everything and found an underground city or premises.
Now I am sure that there are still many secrets hidden in Egypt that can change our modern understanding of the ancient history of the world.