alextrick Not much mystery there...
Just because there was no automated machinery doesn't mean there weren't tools. Bring a whip to one person and you may find a bright idea, bring a whip to many people and find many bright ideas (Sphinx, Pyramids). [not condoning torture or slavery]
As for not understanding how some things are done, back then there wasn't really a patent system. People would protect their trade secrets by keeping them actual secrets. Just because blueprints weren't around doesn't mean that it wasn't designed.
As for the bermuda triangle, for the most part it's all just stories. Fact is, navigational instruments rely on specific information to work, for example waves produced in a certain frequency. Waves in them selves are more of a mystery than the bermuda triangle.
Realizing there are things you don't understand (with a possible yet before that) isn't a mid life crisis. You're learning that there are many things that you don't understand and are becoming more humble, You're questioning what's known and are looking at subjective information and asking questions. Objective information isn't as curious as subjective information because it lacks the potential for deception. Be careful with what you read/hear and think to be true.
But a lot of that boils down to hypothetical thinking and imagination. Theories can run wild and it's the persuit of theories using objective information which has led to the developments of the world today.