Atlantis was very real, and located on what is now the bottom of the Mediterranean sea. It was a deep valley originally that the El-*th dug deeper for a place to secure the energy links of the energy pathways. Because the various aliens used those to get around far more quickly than space vessels, Atlantis soon grew to be quite the bustling metropolis, as it became a support to all those passing thru. The folks waiting for a group to accumulate large enough to warrant the El-*th protection to the next galaxy were very needful of temporary housing and food. Sometimes supplies, like the old west and those going out to homestead.
Most of it was built with raw energy, not solid materials, which is mostly why they can’t find Atlantis, because once the energy stopped supporting them, they vanished. It was all pretty much built that way. I got to see it, as a dragon rider since the greys were based here. It was dazzling. They had a lot of buildings like Russia’s spires, but they were made of translucent energy in shades of various colors, like blown glass.
The pyramids were built by the El-*th as secure bases to hold down and power the connective energy lines they used for transporting themselves and their stuff on world. It was easier than using their own energy. They were much like what held the energy links for the off world transportation lines but when they broke loose in Atlantis, those were completely destroyed.
After Atlantis, those transport functions in the pyramids became non functional and the locals took them over for their various sacred ceremonies, believing them to be places of great power. I think they did have extra power aka energy and probably still do, since no one ever shut them off, if the backlash from Atlantis’s destruction didn’t destroy the powering mechanism.
So my brief take on the pyramids.