Science Fiction

I think my favourite is just when they play with the unknowable. Things so different from humans they operate on different principles and see the world differently.

Sure you see this in fantasy and horror a lot with like the house in House of Leaves or Cthulhu but I'm also thinking the TechnoCore and Shrike in Hyperion, maud'dib in Dune, or the black stuff in the Expanse series. I just like alien stuff that's, well, alien

Okay, absolutely not realistic, but one of my favorites is XANA and Lyoko from Code Lyoko. XANA an AI contained in a nuclear powered supercomputer and is evil. Lyoko is a virtual world within the computer and the only way to stop it. Basically, a group of students at a nearby school have to head over to an abandoned factory where the supercomputer is located and go virtualize themselves into the digital world in order to guide someone who can stop XANA attacks.

XANA is a pretty unrealistic AI villain since it can take control of non-electronic things, control gasses, and even control living creatures. It's a deadly menace that in one episode turned lamp posts into antigravity devices. That kind of unrealistic, yet terrifying AI villain because of just how dangerous it is.

Always fun to come up with horrifying ways that XANA could destroy the world if the main characters ever failed. Or if it was real.

A tardis from Dr who. It's a living spaceship + time machine.

It also has some insane features like:

1. It's bigger on the inside. In fact it has infinite rooms and storage.

2. It also has access to all knowledge across time.

3. It can instantly translate all languages telepathically. So everything you hear and see will automagically be in your language.

4. It can take any form physically. On both the inside and outside. It has a chameleon circuit which makes it blend perfectly into the surroundings.

It's said that it's destiny to be chosen by a tardis. It reads your thoughts and takes you where you want to go or where you are needed.

You might be interested in browsing through this site:

https://projectrho.com/public_html/rocket/

It talks about a lot of sci fi tropes from a hard science perspective, and goes over FTL specifically:

https://www.projectrho.com/public_html/rocket/fasterlight.php

It's kind of a downer site in some respects because it does a lot of "here's why your favorite sci fi series is unrealistic", but in that discussion there's a lot of looking at interesting tropes and concepts. There's also a good explainer for FTL specifically here:

https://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel

I'm boring and I really like rotating megastructures. I think what I find fascinating is they're feasible for us to make IRL if we somehow figure out refining on the moon and mass drivers (ignoring the economics too lol) since they use conventional materials even for relatively large ones.

Everyone is always focused on terraforming or colonizing distant planets. A rotating habitat is engineered to be exactly what we need better than any planet we can colonize.

Life on Mars would be demonstrably worse. You need to bury your habs under meters of regolith to not kill your colonists from radiation. Going outside is a space walk with a laundry list of items you need to attend to with little to no time to enjoy being outdoors (you're in a suit regardless which means it sucks to some extent no matter what)

A rotating Hab means you can live much closer to how you live on Earth

A universe/dimension where everything takes place inside a giant creature can be pretty fun one. The bloom in torment: tides of numenera is the example I recall but I'm sure there's more.

It's so hard to choose just one. Relevan to OP's post is a part of Revelation Space where someone is pushed into a long elevatr shaft on a lighthugger, and she uses the Conjoiner engines to stop her fall relative to the ship, and ends up beating her assailant to death with the floor and ceiling as she adjusted the ship speed back and forth at 10g.

In Adrian Taichovsky's "Alien Clay", there is a planet inhabited by symbionts. Everything is symbiotic with everything else. You'll have a creature, but it's made up of a critter that can digest food, a critter that can see, a critter that can move, a critter that can defend itself, etc.

Neal Asher's "Polity" books depict a future where AI has taken over, and it's a good thing, because humans are such murderous evil dipshits.

"A World Out Of Time" had a guy who was frozen, woke up in the future, was forced into becoming a bussard ramjet pilot, and his attempt to get away from this situation landed him in another, weirder situation. There was a weapon mentioned in this book that would make you wish for death. "If you lie to me, you will take your own life. When I let you."

The Well World, divided up into hexagons, each hex having an entirely different climate, ecology, and technological rules.

"A Deepness in the Sky" by Vernor Vinge had a space faring civilization that didnt use hours, minutes, years, etc. Everything was seconds. Centiseconds, kiloseconds, megaseconds. It made sense for these people who were always in space, always on ships.

Another thing I like is all the various propulsion methods that different authors come up with. Conjoiner engines, is just one example. Niven wrote about a type of hyperspace that moves at exactly one speed, (Or another, faster speed) and looking outside the ship will drive you mad. Alderson drives work instantly, but you have to be in exactly the right spot for it to work. The rest of the time you're stuck with fusion rockets accelerating as fast as the humans on board can stand.

I'm a big fan of Adrian Tchaikovsky's work, but one concept of his that I am fascinated by comes from his book "Alien Clay":

Just give me neon lights in the rain and I'm already happy.

the various forms of FTL, including dimensional teleportation. hyperspace seems quite common between 3 scifi universes. wormhole drives. the most unique seems to be doctors who tardis which uses a form time travel/ftl. that doesnt violate the C velocity, its a way to explain away/bypass, unlike warp drive.

favorite in trek is the vortex drive(xindi,spherebuilders) is similar to transwarp of voth and borg(voth seems to have a more advanced version than the borg since they can cloak at high warp/transwarp which most species can use both tech at the same time, the borg needs a subspace field for thier transwarp and coils), and slipstream of aucturs species.

other unusual ones is the caretakers intergalatic ftl, which uses thier array to produce a wave of energy that makes them pass through a rift, or subspace so almost instantaneous travel.

asgard seems to have the fastest hyperdrives out there unassisted with zpms(although they use massive generators), not even the deadalus class, or even the zpm powered odessey is that fast.