It depends on your age and level of education. Goedel, Escher, Bach was mind-blowing when I was 19. Four years (and some college) later it's a tedious bore. Gabriel Garcia Marquez's "Memories of My Melancholy Whores" is pretty great. Oliver Sacks' "The Man Who Mistook His Wife For A Hat" is full of amazing case studies that will help you construct a personal theory of mind.
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