Oh, I've heard all the alien technology ideas, too. I'm not really willing to put much belief in any of that. Not that I find it hard to believe that we aren't the only things with a conciousness in space.
Other ideas about their far advanced ancient technology include things like this...
http://www.catchpenny.org/abydos.html Granted, I can see flying machines in these, I can also see, maybe, a sarcophagus? Temple walls? A curling stone? Who knows?
There's also the face on Mars theory and the nearby pyramid mountains. The main pyramid in question has some
ridiculously accurate geometry going on but, aren't numbers another invention of Man? Numbers can be manipulated to fit anything, they are merely an 'expression', made by Man to decode the world around him.
The face on Mars can also be split vertically by a mirror; one half and it's symmetrical reflection shows the face of a man - the other half viewed symmetrically shows the face of a lion.
I would like to think, however, that at some period in time, people had an understanding, maybe access to the xx% of brain that we today apparently never use, as a given, just a simple, elegant way that everybody
thought.

We now tend to 'over-think' everything, possibly to make up for the 'base-thought' that we now lack and that would have been taken for granted when this knowledge was second nature, providing the answers to 'How could we build the most amazing, astronomically accurate mark on our part of the Earth?'.
I think I'd like to think that, anyway.
These creations couldn't be built by us today with manpower alone, simple as that. I'm as baffled as the next person. I had some difficulties just making a true-scaled .ter!