Akakor

Akakor is the name of a mythological ancient underground city, located somewhere between Brazil, Bolivia and Peru.
It was described by German journalist Karl Brugger, based on interviews with a self-proclaimed Brazilian Indian chieftain Tatunca Nara in his book "The Chronicle of Akakor" (1976). Although Brugger was apparently convinced, the information's only source Tatunca Nara was later exposed by activist and adventurer Rüdiger Nehberg as being Günther Hauck, a German.
Elements of the story from "The Chronicle of Akakor" were used in the film
"Indiana Jones and the Kingdom of the Crystal Skull", where they were conflated with El Dorado, although references are to "Akator".