Solaris by Stansilaw Lem (1961)
Space faring psychologist Kris Kelvin, arrives on the planet Solaris, a world completely dominated by a mysterious living ocean, to find that the station’s crew have been seeing strange visions of personages from their past. When Kris’ own past comes back to haunt him in the flesh, he strives to determine the purpose of these psychic intrusions and wrestles with the very nature of reality itself.
Most planets in science fiction tend to be some variation of “Earth but purple” with aliens that are “Humans but with more arms.” In Solaris, however, the alien aspects are alien to the point that any earthly reference feels impossible. Lem presents this cosmic mystery with a realism that could trick you into thinking you are reading a genuine anthropological study (complete with long tracts of self-referential academia).
This one is A CLAZZIG and it’s really fun.