Most... alternate... of fictional alternate realities.

Zelazny’s CREATURES OF LIGHT AND DARKNESS is fairly odd.

Yes. I liked “All of an Instant” very much. Garfinkle has an interesting mind (I was on a panel about time travel with him once)

I seem to remember reading a short story which implied a society in which everyone was born male, potentially changing gender as they entered into a relationship.

A bit of googling suggests that is “The Wound” by Lisa Tuttle

Seems to be freely available online here

Stephen Baxter’s Raftcomes to mind. The book is set in a universe wherein the force of gravity is a billion times stronger than it in our universe. Humans (who have a perceptible gravitational field) live in an oxygen nebula in orbit around a massive black hole.

Vernor Vinge’s Fire Upon The Deep is good for this sort of stuff. Featuring a universe with an uncountable variety of different lifeforms ranging all the way up to god-like superbeings, “pack-mind” creatures who are effectively immortal (barring accidents), prosthetically enhanced plant lifeforms on trolleys, sentient computer viruses and a galaxy-spanning internet in which all these (and more) different lifeforms try to communicate with each other without misunderstanding.

One of the best books about aliens, IMHO, is theForeigner series by C.J. Cherryh. Much of the conflict is caused by the dissonance of aliens that superficially resemble humans, but think and react differently.

Pyramid Scheme and its sequel feature a parallel world that really works the way the ancients understood it. Besides all the gods and monsters, if you fire a gun in that world, instead of a chemical reaction, a small demon tries to push the bullet as fast as possible (this is not very effective).

James Tiptree, Jr. “Love is the Plan the Plan is Death” is told from the POV of aliens who are quite alien. I was also blown away by the alienness of the aliens in Octavia Butler’s Xenogenesis trilogy, who conquer Earth… only they don’t really have the concept of hierarchy, so they have a completely different conception of it. Highly recommended.

I also really like Ted Chiang’s “Story of Your Life,” which postulates aliens that think about things in terms of the principle of least action rather than cause-and-effect, which shows up in their language as well. (It does take place on Earth, with a human linguist who is trying to understand the aliens.)

Is this “principle of least action” as in the technical physics term, or a layman’s understanding of “action”? Because if the former, that could be a fascinating book to read, albeit not very widely accessible.

I was going to mention a vaguely remembered story where the characters were geometric shapes but I am 99% sure what I had in mind was Flatland mentioned elsewhere.

The Alternate history I have read that is the most divergent but still could be called alternate history was West of Eden.

The premise was that the dinosaurs never died and in the Old World evolved into an intelligent society based around organic genetically engineered technology. In the New World, specifically North America, primitive humanoids evolved. The story is the ensuing culture clash.

The Night Land written in 1912 by William Hodgeson. It’s almost impossible to describe. The sun’s gone out in the far future and all of humanity is gathered in one city. But there are… things… in the dark that come from beyond the Universe.

It’s been many years since I’ve read it, but Einstein’s Dreams by Alan Lightman had a similar setup—in one chapter, at least. Each one featured a version of Earth where time operated completely differently. Not a bad read.

The physics term. It’s a brilliant story.

There’s the novels of China Miéville set in his Bas-Lag universe - Perdido Street Station, The Scar, and Iron Council. The universe contains ideas from numerous other science fiction and fantasy universes thrown together willy-nilly. Despite this, the plots aren’t at all light-hearted and optimistic. They’re gritty and pessimistic.

For that matter, even though they’ve been around so long that we don’t think of them as strange, *Alice’s Adventures in Wonderland *and Through the Looking Glass by Lewis Carroll are set in an excruciatingly weird universe.

In the Lovecraftian vein, I thought Woman Between Worlds was pretty out there. It concerns a woman from another dimension who is invisible in ours and so gets a full body tattoo to be visible here. Eventually there is a trip to the other dimension which is somewhat different.

One native species. The “species” with the three “sexes” is the juvenile/reproductive phase of the other. After they finish reproducing, the three sexes merge into the other “species”.

China Mieville’s noir thriller The City And The City has the premise that two cities in modern-day eastern Europe share the same physical space and time, but the citizens are forbidden from seeing each other or the architecture of each other’s city - other than via a carefully controlled checkpoint.

This isn’t really relevant to my statement – I’m talking about psychology, not physiology.
Besuides, I’ve written many times on this Board that the point of such rubber forehead makeup isn’t even that you’ve got two eyes and a forehead – it’s so that the human actors can show those and use them to emote.

Yeah. Was trying not to give too much away.

I believe the art of Richard Powers fills the bill here. He made cover art for SF paperbacks in the 1960s that to my mind did a better job of portraying the alienness of the universe better than anyone else.Here are a couple of images and some links to galleries of his work. He was influenced by surrealism, but hardly limited by it … he had a knack for combining surrealist landscapes and images with more prosaic images to convey a sense of humanity on the edge of the knowable. I wish most of the novels he did artwork for had been 1/10th as good as their covers. They would have been damn good reads!