Hitler's palace
Based off classic Journey to the center of the Earth design, the Hollow Earth is a large underground cavity. It has a jungle climate and is populated with dinosaurs and lizard people.
In Iron Sky: The Coming Race: the entrance to the Hollow Earth is found in antartica, which was also the launchpad for the Nazis journey to the moon. At the center is the city of Agartha, the crashed Vril Spaceship, and the Vril energy source. Living in Agratha are all of histories greatest leaders who were secretly shape-shifting reptilians.