The Hollow Earth theory is a concept suggesting that the Earth is not a solid sphere but instead contains vast, empty spaces or even entire civilizations within its interior. Proponents of this theory believe that these inner regions could be inhabited by advanced beings or unique ecosystems, often drawing on myths and legends from various cultures. This idea gained popularity in the 17th and 18th centuries, with notable figures like Edmond Halley proposing that the Earth consists of concentric spheres. Although the theory has been largely discredited by modern science, it continues to capture the imagination of some and appears in various forms of popular culture, including literature and movies.