Been geeking out on the pyramids in Egypt lately. None of the standard explanations have ever made sense to me. From an engineering point of view, their existence is simply impossible with what we know about what was available to us at the time they were built. Hell, it would likely be well neigh impossible to build them even today, with modern methods and technologies. The sheer mass of some of the blocks (80 tons!) along with their precise, almost air-tight fit in some of the inner chambers. No way was this done with the tools of the day.
So, here is an interesting, and quite different take on at least the first one, the Great Pyramid of Giza. Its construction is, from an engineering and architectural standpoint, superior to those that followed. Much more precisely fit, especially in those critical inner chambers. These folks contend that this is due to the fact that it was first, and was the only one built by the original architects, with the others being later attempts to duplicate its functionality.
What function would that be? How about the production of plutonium. These folks make an interesting case for that. Kinda long, but worth the read.
https://originalscientist.blogspot.com/2013/05/were-pyramids-nuclear-reactors.html?m=1