In one copy of a 1942 edition of German historian Gert Buchheit’s biography of Rainer Maria Rilke, someone has glued a typewritten and hectographed alphanumeric text. The text fills 33 pages with 18,760 characters in groups of four. Analysis shows that it’s less ordered than English or German but more ordered than random text. To date, no one has been able to make sense of it.
Here’s the cryptogram itself, and here’s an analysis.