Where It All Goes Down
Solaris
Solaris is set on a space station hovering near the surface ocean of the planet Solaris. Solaris the planet is mostly ocean, and the ocean is maybe sort of sentient—scientists think it's a kind of big brain, which could be controlling the orbit of the planet.
You don't necessarily get a strong sense of place in ether the space station or on Solaris itself—but that's perhaps part of the point. Again, Solaris is a brain, and going to Solaris, therefore, is less going to a particular place than going into a head—perhaps Lem's, perhaps yours, perhaps someone else's.
This is most clear when Berton describes flying over the Solaris ocean, circling through the fog and suddenly coming upon:
[…] something which looked like a garden. Yes, a garden. Trees, hedges, paths—but it wasn't a real garden; it was all made of the same substance, which had hardened and by now looked like yellow plaster. (6.180)
We eventually learn that the garden is probably something from the mind of Fechner, a pilot who committed suicide by leaping into the ocean. Solaris has become, more or less literally, Fechner's mind; the landscape is his dreams. In flying through Solaris, Berton is flying through Fechner's head.
Again, this is an obvious instance in which the setting is a brain or a dream. But you could read virtually all of Solaris this way. For instance, early in the novel, Kelvin is wandering around the station and muses that:
I had never lived on the Station, but during my training on Earth I had spent six weeks in an exact replica of it; when I reached a short aluminum stairway, I knew where it led. (4.1)
Kelvin has been on the station before he's been on the station—the station is in his head before he's in the station. In coming to the station, then, he is entering a memory; the image in his brain of what the station is like. The setting of Solaris is the interior of his mind—which is where he finds Rheya.