MSD

It has been. Ground-penetrating radar has been used and a network of tunnels and rooms has been located under a paw of the Sphinx. The Egyptian Government refuses to allow excavation, and has forbidden some of the researchers who found it from entering the country. It is widely suspected by conspiriologists that this is the hall of records of the Egyptian branch of Freemasonary. If the Masons were around back then, they would be a prime suspect in the mystery of the pyramid's creators. Or, it's possible that all of the plans for the pyramids were deposited in the hall of records and sealed under the Sphinx.

Additionally, the Sphinx shows signs of erosion that indicates rain damage, and completely inconsistent with expectations of wind and sand erosion. Egypt hasn't been a wet landscape for thousands of years before those widely believed to have built the pyramids settled the area. It is probable that the Sphinx, and possibly the pyramids, were built before they settled there. If I was looking for a place to settle while walking across the continent, and I found pyramids and a sphinx sitting there in the sand, I'd conclude that the area had some sort of significance and sit my ass down right there and build a civilization.