Agharta

The first human race Aryan, was race of Agharta that being sent by Agharta priests to help mankind to be civilized. So they create first religion called hindu, by writing Veda, that tells about precepts, rites, stories of gods, and knowledge.
Through this literature, people starts building civilization, homes, vehicles, etc.
Agharta is a race that so mysterious that nobody know their origin. Shambala is not Agharta. Shamballa is people on earth that migrate to Agharta (their location is under Taklamakan Dessert). They migrate to Agharta after their first king Suchandra prophecise about the rise of islam that someday will invade India.
Even Islamic people want to come to Agharta too later.
Most people think they are living on earth, and Agharta people are living inside the earth. But based on buddhist and hindu cosmology, we should be inside, not the outside. above us is Mount meru, land of 33 gods, and above Meru is Heaven, which is Agharta. So we are in the inside.
When admiral byrd from america came to Agharta, the agharta leader said "welcome to interior side", but I think that just a trick because admiral byrd still not ready to be told the truth.
Since our sun and moon are artificial, it is acceptable that we live inside earth.