For years, I've had a "for fun" theory about one type of dinosaur achieving sentience and leaving the earth. They redirect a large asteroid to smash into the land mass later legends will call "Atlantis" which destroys all traces of their civilization.
These dinos return from time to time and pull human up to see what sort of life evolved after they handed over the keys, so to speak. Some of those tests included things like Stonehenge, Newgrange, and Maes Howe in the British Isles, and Serpent Mound and the Nazca Lines in the Americas. None of these structures have any purpose you see. They were constructed by the aliens as a type of psychological experiment to see what the future beings would think they were.
If you want to use that, feel free to adapt it however you like.
I'm Not Evil.
An evil person would do the things that pop into my head.