Because they suspected that our surface is on the interior of a concave Earth, Hitler sent an expedition, including Dr. Heinz Fischer and powerful telescopic cameras, to the Baltic island of Rugen to spy on the British fleet. Fischer did so not by aiming his cameras across the waters, but by pointing them up to peer across the atmosphere to the Atlantic Ocean. The expedition was a failure, of course. Fischer's cameras saw nothing but sky, and the British fleet remained safe.
Escape to Antarctica
Then there's the legend... that Hitler and many of his Nazi minions escaped Germany in the closing days of World War II and fled to Antarctica where at the South Pole they had discovered an entrance to the Earth's interior. According to the Hollow Earth Research Society in Ontario, Canada, they are still there. After the war, the organization claims, the Allies discovered that more than 2,000 scientists from Germany and Italy had vanished, along with almost a million people, to the land beyond the South Pole.
This story gets more complicated with Nazi-designed UFOs, Nazi collaboration with the people who live in the center of the Earth, and the explanation for "Aryan-looking" UFO pilots.
While the evidence for either hollow Earth theory is close to nil (although some folks claim to have proof in the form of photos), the story involving Nazis, war, and the romance of exploratory adventure sounds like the makings of a great Indiana Jones story. In fact, it is! In the novel Indiana Jones and the Hollow Earth by Max McCoy, Indy comes into the possession of a mysterious journal hinting at the existence of an underground civilization that he and the Nazis race to find. The fate of the world - hollow or not - is in Indy's hands!