Solaris

Who's testing whom? When Kris Kelvin arrives at the planet Solaris to study the ocean that covers its surface, he is forced to confront a painful, hitherto unconscious memory embodied in the living physical likeness of a long-dead lover. Others examining the planet, Kelvin learns, are plagued with their own repressed and newly corporeal memories. Scientists speculate that the Solaris ocean may be a massive brain that creates these incarnate memories, its purpose in doing so unknown.
The first of Lem's novels to be published in America and now considered a classic, SOLARIS raises a question: Can we truly understand the universe around us without first understanding what lies within?