Have you read The Emerald Tablets of Thoth the Atlantean?
<a href="https://brotherhoodofthewhitetemple.com/the-emerald-tablets/">https://brotherhoodofthewhitetemple.com/the-emerald-tablets/</a>
It's an interesting text, apparently 36 000 years old.
It has some info on the pyramid and the sphinx.
In short, Thoth traveled from Atlantis when it sank, and went to Khem (Egypt), to bring wisdom to man.
He traveled by spaceship and hid it under the sand, and created a big sign of a lion on top of it.
The pyramid was constructed upon the entrance to the Halls of Amenti, where the 7(or 9) Lords of Light is located.
And inside there is a stone coffin, where the priests can lay down, and their mental powers will be amplified.
Below the pyramid is a tunnel that is blocked by a big stone, this can be opened by he who has the key (not a physical key), and this tunnel will lead to the spaceship under the sphinx. The spaceship also contains the library of Atlantis, and the ship is suppose to be dormant until man will need it to fight off invaders from other worlds.
Im not done with the book yet, so I dont know what the key is yet, but I assume it is knowledge of some sort.
The esoteric information in this book is also in line with what I read in Seth Speaks, by Jane Roberts, which is also a very interesting read.