Up until very recently I used to believe that monuments like the pyramids could only have been built with the help of a civilization far more technologically advanced then ours. The scale of the undertaking presents a problem: Even with modern technology it would be a massive endevor so I still have my doubts that the great pyramids at Giza were built by slaves alone. There are means of technology that I think the ancient egyptians had knowledge of that we have lost. Consider Coral Castle; as for the incredibly precise measurments encoded into the pyramids, that's a facinating story.
Looking at the Summarian legends of gods coming down to interact with mankind and similar mythologies told around the world in indigenous cultures I still think that there is something to the idea of alien intervention in human history and probably even our creation. Yet I still have a notion that we are a far more capable species then modern technologically "advanced" wisdom would have us believe.