Recently Ive came across with this and it’s more interesting me rather than aliens:
https://www.bibliotecapleyades.net/tierra_hueca/esp_tierra_hueca_2d.htm
The claims from Admiral Richard Evelyn Byrd, the man who saw the first north and south poles top from plane. And he said that when they went research for north pole, he met with agarthians very advanced humans, and story goes.
What do you think about this and also some people say there is Shambala and they are evil, bad and enemies of Agartha, and others say Shambala is capital of Agartha, or it is the difference names for same civilization