Ancient Aliens: Who lives in our Hollow Earth?

Pat Macpherson, Dhr. Seven, Wisdom Quarterly; Ancient Aliens, History Channel (History.com)

Ancient Aliens episode "Underground Aliens" on subterranean cities built by ETs ("the gods")

Ancient Buddhist stupas (burial mounds/reliquaries) are shaped as mandala-pagodas that represent the form of the cosmos. Pagan (Bagan), Burma (Azimuddin Ibrahim/flickr.com).

Buddhist cosmology: 31 Planes of Existence with beings in worlds below, devas up in space.