It’s so hard to choose just one. Relevan to OP’s post <spoiler>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.</spoiler>

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.