In your mind, what event qualifies as a genuine unexplained mystery?

I am looking for objective answers here and not lunacy (I know I came to the wrong place). As a scientist; historically I have often scoffed at the myriad of UFO crackpots that populate non-primetime TV. However, I have taken a fresh look at some of these mysterious events in recent years, and will admit that some are difficult to explain away by deductive logic. JAL 1628 over Alaska, the Belgian UFO wave etc – what are some of your favourite mysteries.