Solaris by Stanislaw Lem. A psychologist is sent to a station in orbit around a planet covered by a sentient ocean to determine if research on it should continue. Lem's work consistently blows my mind, actually--other favorites are His Master's Voice (memoirs of a mathematician working on a project to decipher what might be a message from extraterrestrials) and Peace on Earth (an adventurer returns from a trip to the moon with his brain bisected, and the half that remembers what happened is both unable and unwilling to communicate it).
Solaris by Stanislaw Lem. A psychologist is sent to a station in orbit around a planet covered by a sentient ocean to determine if research on it should continue. Lem's work consistently blows my mind, actually--other favorites are His Master's Voice (memoirs of a mathematician working on a project to decipher what might be a message from extraterrestrials) and Peace on Earth (an adventurer returns from a trip to the moon with his brain bisected, and the half that remembers what happened is both unable and unwilling to communicate it).