Just to clear things up a bit:
Reptilians were the original sapient dinosaurs, even had a civilization before the extinction event, some went underground, some went to space. 65 million years later, ancient aliens including the now malevolent space reptoids (who have traveled pan-dimensionally at this point and now have brought their stronger draconian brothers to take earth back), arrive and use magic mushrooms to evolve apes into thinking beings, we help them mine gold for a bit then for hundreds of thousands of years we develop our own society, with the underground reptoid below us, who have opened or "found" a portal to an alternate universe where the earth is hollow, so Agartha is more like a place inside our "real" molten earth in another reality, like a portal or an isekai world, and the humans make a few civilizations that rise and fall, we make giants and dragons and all sort of genetic monsters but basically we keep fucking up, last time was Atlantis, btw there's also Martians who may or may not be related to us in the same gengineering experiment way, well 1 million years ago Mars gets btfo and they wreck their shit and some come down here and mate with us which was also part of us evolving from apes to man, so anyways Atlantis collapses from the great flood caused by the meteor impact in Greenland 13,000 years ago and we basically have to start from scratch again, and that leads up to now. Ancient aliens try to keep our planet a prison planet for souls to reincarnate to, Earth is a fucked up violent school for souls, there are many angelic, utopian alien civs out there, but also way worse demonic hell worlds for evil aliens, anyways the DMT machine elves and the sentient pan-universal mushroom network wants to help us out, so we have already been exploring and colonizing space (again) since at least the 50s, we have been to Mars and beyond, there are American astronauts exploring the solar system and even the galaxy right now with reverse engineered alien tech, and apparently the USA is 6 million years ahead of the other nations of the world technologically thanks to secret deals and treaties we have with aliens, such as ayys being allowed to abduct Americans (a reason why you pretty much only see abduction accounts in America). Oh also DMT and high dose psychedelic's are somehow highly related to how the ancient aliens tech and ufos work, they are highly related. Oh and ghosts are obviously real too, demons, angels, all of the world's religion's gods and their various heavens and hells you can imagine are real at least as egregores, if not connecting back to some pan-cosmic archetypal forms, and the Fae are also very real and their realm is accessible by anyone foolish enough to wish to enter into it, they may be our ancestors spirits in a way but their world is very real and right next to ours. Reality is more flexible than brittle, in my eyes, and you can find yourself in a liminal space leading somewhere unknown easier than you can tear a hole in spacetime. Also, many worlds theory and infinite multiverse theory are real, so Batman, Godzilla, and Tony the Tiger are all equally real, somewhere out there.
Edit: I also forgot to mention that some of those pre-Atlantean civilization cycles were basically the stories and histories told in The Lord of the Rings, uncovered by J. R. R. Tolkien in ancient texts at the bottom stores of Oxford libraries, and that the Fae may be the ancient spirits and ghosts from those times.