A Fata Morgana is something that isn't. Like a mirage, it's a trick of light and atmosphere, usually seen over water, but more elaborate than that. Mountains turn into boats and then majestic castles, then just sort of erode away, so you are not sure which image was real. I don't think I've ever seen one except in a movie. It's one of those sights which likely evoked terror in ancient humans, when no one understood why an entire ship was hanging upside-down fifty feet above the surface of the water. And why that same ship then slowly turned inside-out and sank into the ocean.
In every video of a Fata Morgana I could find, there is a big argument in the comments section about whether it is a Morgana or (in fact) a mirage. I don't care. It's a weird, cool, slightly spooky thing, a thing we can clearly see but which actually doesn't exist in the form we're seeing. Who or what is playing this eerie trick of distortion on our eyes and brain?
I use this video not so much because it's a good example (though it is that), but because of the beautiful noise of the surf, the utter lack of captions, and the beach-dwellers casually romping while the bizarre illusion plays out in the distance. The gifs were just lying around in my file, left over from another post.