Forgotten Fatherland: The Search for Elisabeth Nietzsche, by Ben Macintyre (1992).It sounded fascinating at the time, and still does, so yesterday I obtained the book from the library. If you've read it, please feel free to comment.
The intrepid Macintyre took a boat trip into the Paraguayan jungle in 1991 in search of the surviving inhabitants of Nueva Germania—an abortive "Aryan" colony founded in the late nineteenth century by the ghastly Elisabeth Nietzsche, racist sister of the philosopher. He found a weird village of unreconstructed white supremacists—inbred, half mad, many of them still speaking a kind of zombie German—and heard some curious and frightening stories about Josef Mengele. A true-life Heart of Darkness.
And yes, my TTD folder does have items 18 years old. Sigh...
Addendum: Hat tips to Hero for Hire and to Bub for leading me to this related video from Vice: Vice link.
Addendum #2: See also this link found by Mark.