Hello dralex. Have you heard of Corey Goode?
He claims people/beings are living under the earth's crust.
He doesn't describe it as an earth that is hollow with a central sun, but rather many large caverns mostly created through volcanic, ice and other earth processes. He claims some of these caverns are the size of states where thousands live and some sort of bio-luminescence seems to be used.
He also mentions many large caverns in Antarctica where lost civilizations lived and current military bases exist.
It is interesting that our last president, secretary of state, the pope and many other prominent people in our world have recently traveled to Antarctica to visit for some reason.
Some people say that some Atlanteans would have migrated to the center of the Earth before the strong catastrophic event that tilted the Earth's axis a few degrees. Event caused by experiments with telluric forces. And there is another race living in a shallower potion, less evolved beings living in caves as you say. When someone see flying saucers (which are multidimensional) fading behind the mountain, these objects are actually traversing into it for these deep locations. But we have no way of knowing what is true, especially if have interest of governments. I'll research about Corey Goode, it's a very interesting subject. Thank you.