The earth is hollow, the 2 main entrances to it are the poles. There are also secondary entrances in innaccessible places as the uplands (ex: Unterbberg) or in some deserts as the desert of Gobi, bermuda triangle,....
It's also called Agartha, inner earth, middle-earth and its capital is just above the Tibet and is named Shambahala/Shamballa. That's why so many personalities go there and that'y why this apparently insignificant, is so disputed.
I am not the author of the 2 following series. I do not agree with all what is said (that Muhammad was a demon and about the author's promotion of the new age, I really don't share his views, Allah and the Quran are our only Truth and Light and Guidance ). These series are just interesting from a practical point of view, you can see clear evidence of the existence of a hollow earth inhabitated by all kind of demons.
Satan and his Army of demons (orcs, reptilians, all kind of human/Jinn hybrids, monsters) live there.
The so called Aliens are not from outer space but live in the inner earth.
Aliens = devils = Jinns = sheytans = demons = shapeshifters = Masters of illusions = Space Brothers.... The devils have many identities, many names, but you recognize them by their behaviour which is opposed to the Laws of Allah which are contained in the Torah, the Bible and the Quran prevails)
Dhul Qarnayn, the special servant of Allah, has jailed Gog and Magog in the hollow earth and has closed the 2 main entrances which are Artica and Antartica.
That's why the poles are no-fly zones and that's way in some places, high eletromagnetic fields prevent any plane or ship to approach, like the Bermuda Triangle.
But Allah has also said that Gog and Magog will be released one day and will be spread all over the world so far they are numerous. Don't forget that the surface within the earth is far superior to the surface on the earth.