Do you believe that the earth we live in is hollow? and that there is another advanced civilization there?
Why don't you go and ask flat earthers is earth hollow?
I am sure they will find some pictures and videos on youtube
Flat earthers are a special kind. If I go straight in one direction will I reach a wall? Or maybe there's a cliff and I'll fall into the void? I also heard a theory that all governments are blocking The Poles, and you can't go there, because that's where Earth ends