Iain M. Banks's Culture novels do have some Nightmare Fuel. Given that at their core, they are about a utopian civilization, this is surprising.
As a Moments subpage, all spoilers are unmarked. You Have Been Warned.
- Look To Windward features terrorists from a civilization the Culture caused a civil war in trying to get revenge. They fail, and the Culture get revenge in the form of a nanotech construct. The first terrorist is ripped apart from the inside out be a swarm of nanotech bugs. They're only on the inside because they forced their way in through his mouth and eyeballs. The second terrorist is flayed alive by the construct, then pushed off a cliff while it still holds his intestines. The moral? Don't fuck with the Culture.
- Consider Phlebas featured that horribly obese cannibal and his strange cult.
- Also in Consider Phlebas, a war that lasts 38 years and kills 851.4 billion people is described as a "small, short war."
- In Excession the Affronters genetically modify living beings into literal playthings, such as balls for a tennislike game.
- They genetically modified females of their own species so they find reproduction incredibly painful.
- The entertainment on Azadian TV consists of horrible, sexualised torture in The Player of Games.
- The Chairmaker in Use of Weapons has the skeleton of his former lover, his adversary's sister, turned into a small chair, which he arranges to have delivered to his adversary! As if this wasn't horrifying enough, it has a particular effect on the protagonist because it resembles the chair he once walked in on his enemy, once a childhood friend, having sex with her on. It is also implied, but not outright stated, that he had at least a tuft of her pubic hair left on the finished product.
- In the same book, the description of Cheradanine's brain surgery borders on this and Nausea Fuel.
- The Iln warrior-ship from Matter. That such an entity can arrive in the last fifty pages of the book (although not without build-up) and unseat the story's until-then main antagonist as the most disturbing character in the book in a few short paragraphs is no mean feat.
- The Hells in Surface Detail are designed to be this in-universe, and based on some Nightmare Fuel dreamed up by real-life religious fanatics and some bizarre transhumanists.
- The statement that some of the earliest civilizations to abolish their Hells only created them in the first place because they thought that was what was done and didn't want to seem backwards says some pretty frightening things in itself.
- "Aggressive Hegemonising Swarm Objects" in general are this both in and out of universe, and there's a specific Culture group dedicated to dealing with them.
- In Surface Detail, there's a direct mention that the thought of remnants of such entities ending up in an advanced manufacturing plant left behind by a Sublimed civilization is the kind of thing that would disturb the sleep of even the notoriously laid-back Culture, especially those who deal with them on a regular basis.
- Then there's the fact that the factories and computational assets in question might soon be used to bring a virtual war into the Real, and may already be involved in simulating Hells, which just takes the whole thing up to eleven.
- Uagen's murder by a Chelgrian in Look to Windward, described from his own POV, is absolutely over-the-top both in its brutality and Banks's lovingly detailed description.
