Akakor

Akakor is a fictional ancient underground city somewhere between Brazil and Peru. 
The German journalist Karl Brugger described the city in his book "The Chronicle of Akakor" (1976). Information about the city is from an interview with Tatunca Nara, a Brazilian Indian. Tantunca Nara speaks about possible contact with extraterrestrials in the ancient past. He says these extraterrestrials are believed to have built this mysterious city. Two similar cities are mentioned in this book - Akanis and Akahim. 
Later Rüdiger Nehberg showed that Tatunca Nara was actually a German named Günther Hauck.
Parts of the story from "The Chronicle of Akakor" were used in the movie "Indiana Jones and the Kingdom of the Crystal Skull".