Marshall B. Gardner’s A Journey to the Earth’s Interior (1913, 1920) is a pseudo-scientific treatise arguing that the Earth is hollow, featuring a central sun and openings at the poles. Gardner challenges 20th-century polar explorations, suggesting that explorers like Peary didn't reach a north pole, but an opening leading inside. Gardner’s work is recognized as a notable example of early 20th-century hollow-earth literature, aiming to provide a "scientific" explanation for his claims, contrasting with earlier, more fantastical tales.