1. My first idea for the Pyramids of Giza revolve around the Gods themselves. The pyramids are supposedly built as great tombs for pharoahs, and Osiris is the god of death. I think that a fun story could be made where Osiris is playing a prank on Isis by stealing one of his favorite humans and trapping him in this tomb, which turns out to be a marvelous structure.
Source: The Story of Isis and Osiris, Schofield, Freebookapalooza
2. My second idea is more of a science fiction idea. It would revolve around a scientist, who comes across a startling discovery. There has been much controversy surrounding the pyramids, and this scientist reveals his discovery that the pyramids match the layout of Orion's belt, which he had only recently discovered (this is true). He goes on this massive quest to the center of the Great Pyramid, and when he gets there, he is whisked away to the past where him and his team are found to be the architects of the pyramid, who have travelled from the future. It turns out to be an endless loop, but he realizes that the pyramids were not built by aliens, but rather by himself as a tool to help humanity.
Source: Orion correlation theory, Wikipedia
3. My last idea revolves around the famous alien conspiracy theory. The pyramids were built with technology far too advanced for its time, so they must have had help. It was discovered that the location coordinated for the great pyramid are exactly that of the speed of light, which was not discovered until much later. This can be tied in to aliens traveling via the speed of light (ie. time travel) to clue humans in about their existence, because the Egyptian gods have taken wrath on them and they need humanity's help. I like the idea of an amicable relationship between humans and aliens.
Source: Time Travel and the Great Pyramids, Express UK
The Great Pyramids of Giza, Wikimedia
Some storytelling ideas I could use includes a first person narrative, by creating a character that lives during these events. Of course, I could also use the less personal third person approach, but I want to avoid making the stories sound like a history book.