The Anunnaki were ancient astronauts who visit Earth periodically, like every 10 000 years or something like that, I don’t remember the exact frequency, but they are supposed to visit us again some time in the future, when it’s their time for a new visit. They are so handsome that we can’t resist mating with them and the current human race is a cross between the Anunnaki and the humans of the last time they visited us.
If you travel far enough north, you will find a hidden civilization living under the ice at the North Pole that they don’t want us to know about.
The first one sounds like it would make an interesting premise for a sci fi series.
And the second is the premise of several Christmas movies.
Hey, I recently read about that second one in a Mark Lawrence book.