What's the best book no one has heard of?

Drop me some great books you've read that are obscure please...looking for new things to read (am a former librarian so I've read a lot of books)...any genre but must have an English version at least (I don't read very well in other languages unfortunately). I'll even leave one for you guys: Faith, Madness and Spontaneous Human Combustion by Gerald Callahan...it is about immunology and self perception...the tie in to immunology is written in such a way that it isn't overly technical. It is a beautiful book that makes you think about things (as any good book should). It can be a bit hard to find but it is on Amazon and the kindle unlimited version is free.