The Algorithms at various social media platforms are so sketchy and enigmatic, that they have become of interest to congress and civil libertarians.

The Nazca Lines in Peru remain an enigma as the geoglyphs were made by a pre-industrial civilization for view from the sky, but they did not have any form of air travel as far as we know  

The ultimate enigma is the human relationship with the unknown and the human gullibility to permit a select few to come up with somewhat credible answers and dubious rules and requirements (temples, monuments, sacrifices, etc.) in exchange for a free ride through life.