I’ve long been fascinated by the Antikythera mechanism and what it could have been used for, how it was built, etc. Now, an interesting article, An Ancient Device Too Advanced to Be Real Gives Up Its Secrets at Last, gives some possible insight.
To be fair, though, I’m also fascinated by the Nazca Lines in Peru, I once did a diorama project on my explanations for the Bermuda Triangle, and have gone looking for The Loch Ness Monster (not in any organized official way, but I did take a tour boat out onto the water). Pretty much any unexplained phenomenon is okay in my book (and I’m really excited out new cable package included The History Channel in English!)