Solaris by Stanislaw Lem

Solaris was first published in 1961. It is older than most of its readers, but the story has not aged in the least. It is perhaps because it doesn’t rely on trickery, gadgets and mimicry. Its concept is utterly original and reaches beyond the confines of its sci-fi genre.
A psychologist, Kris Kelvin arrives at the space station on the planet of Solaris shortly after one of the scientists based there takes his own life. Immediately upon his arrival, strange things begin to happen. He sees a naked, athletic black woman who cannot possibly be there. Soon, Rheya, his long gone lover, makes an appearance, and will not leave his side. She too cannot be real but all his senses, and his memories, tell him that she is. Two other resident-scientists experience similar … hallucinations? encounters? relationships? It’s difficult to define.
This “resurrection” of the long-dead lovers can only be attributed to the planet of Solaris, and more specifically to the ocean that inhabits it. The ocean covers the entire surface of the planet. It appears to be a living, organic form which has evolved to such an extent that it is capable of thinking, creating, understanding and probably penetrating into man’s mind to retrieve his memories and to use them to recreate people from his past. This doesn’t seem entirely innocent – it may be that those “visitors” are spies or even assassins, although they claim to be benign and act innocently enough. They cannot be killed or sent away – they keep coming back. And more importantly their personalities evolve and they are able to form genuine relationships with “their” humans.
“Solaris” explores not only the depths of the universe and the diversity of matter/creation, but even more intriguingly the depths of human mind, its secrets, memories and its self-awareness. The book is about the new and unexplored frontiers, our soul being the most remote and the hardest to comprehend.
Brilliant, intelligent book!