I have come across an interesting quote of the 15th century alchemic writer Basilius Valentinus (Whoever he was) It is one page 100 of the book Esoteric Astrology by Bepin and Maduri Behari. It is of interest to us and suggests that Europeans of those times knew of the hollow earth and the inner sun. They knew that mother earth was a living entity and not composed of dead matter, which indicates that, back then, they had superior knowledge as compared to modern scientists, who can be more complicated than knowledgeable.
"The Earth was not a dead body but inhabited by the spirit which is the life and soul of the Earth. All created things, even the minerals, receive their powers from the spirit of the Earth. The spirit is life, it is nourished by the star [the Sun, the inner sun?] and gives nourishment to all living things which it shelters in its womb".