Explain the mystery of the pyramid at the Giza

The mystery of the pyramids is how whey were built. The fact that a civilization 3000 years ago erected something that both still stands, and we can't explain how it was built. We have ideas on how they cut the stone, moved it, and scaffolded the building, but we just don't know how they made those methods work within the allotted time frame. We're not even certain if we can match that construction in the same timespan today, so it really boggles the mind that Ancient Egypt did it thousands of years ago.