Definitely House of Leaves. A story inside of a story, inside of a story, with all narrators being just a bit crazy. Text of different fonts, going all over the place and even upside down based on the story. Just make sure to get the physical copy.

Not a book, but a webcomic: https://elan.school/

Be careful what you wish for OP, this is THE WILDEST shit you will ever read (at least top 5, guaranteed) and the worst/best part is that it's all true.

Also, its VERY addictive so clear your schedule.

You've been warned.

You've ALL been warned.

I went into Do Androids Dream of Electric Sheep? blind. Hadn't seen the movie, hadn't read any other Dick, hadn't even had it hyped to me by a friend. What a series of mindfucks.

Fear and Loathing in Las Vegas is an obvious but nonetheless relevant answer. What a ride.

Also Infinite Jest.

I'd say the first book of The Chronicles of Thomas covenant the unbeliever was a wild trip.

In the story, Thomas covenant has leprosy. Due to the leprosy he is numb from the neck down even though he can still walk. He has no sensation when he touches anything and he cannot engage in his chosen profession which is writing. In a fit of pique he rescues a girl that almost gets hit by a car and gets isekaied.

This was written in the late '70s so it was not a common trope at the time.

He arrives in a world of magic on top of a mountain covered in Giant steps, he crawls his way down the mountain and encounters a girl who uses the magic of the land to heal him of his leprosy.

Believing this is all a dream and trying to prove to himself that this is not real, he rapes the girl.

The girls seems very distraught but pulls herself together and guides him into town and that is when he discovers that the white gold wedding ring on his finger is the source of wild magic.

There is a great evil on the land that plans to destroy everything and he is the chosen person, the only person who can stop it.

He has to fight against his disbelief of the world while reconciling his abhorrent actions with his own internal sense of morality in order to have a chance to go home again.

This book spawned a 10 book series covering hundreds of years of history in the land with Thomas Covenant's battle with the forces of evil and the lives of the people of the land resting in his leprosy numbed hands.

It's an amazing work but it is a rough read.

China Miéville - The City & the City is one that I don't think I'll ever forget. Wild because as far out as it feels, it's also a pretty accurate portrayal of how we've trained ourselves to intentionally not see. I find myself thinking of the book often.

The Road. Still think about it a lot.

Philip K Dick - The three stigmata of palmer eldritch.

It's like a dream, where you forget where you came from, but at the same time there are powerful themes that are personally and emotionally affecting. Like an acid trip or religious experience, you aren't the same person after you've finished it, whatever lesson you got from it.

The Book of Rack the Healer by Zach Hughes was pretty wild.

It's 'New wave' sci-fi from the 1970's, and revolves around these mutated humans in a deeply poisonous and radioactive world where it's forbidden to dig into the earth.

The humans have evolved a carapice and internal air sacks that they fill to hold their breath before leaving their safe organic dome homes that change color depending on their mood. Some of the domes have women in them that don't seem capable of complex thought, and live purely through sensory input, are telepathic, and are basically constantly edging themselves all day.

It's a drug fueled fever dream, for sure.

Naked Lunch. It's a dark strange read but it suck with me.

Strange new world by Heinlein.
Martian Jesus comes back to earth and is like, wtf guys?

I’m not sure if it’s the wildest but the first that comes to mind is “John Dies at the End”

The one that included the most wildlife might be hard to know exactly, but 'The Lost World' by Arthur Conan Doyle might be a contender.

One of my favourite books, and one that gave me lots to think about was His Dark Materials by Phillip Pullman.

The most 'different' setting for a book that I've read might be The Planiverse by AKA Dewdney, which takes place in a 2d world with thought out and realistic physics and societies.

Perdido Street Station by China Mieville. I into it blind.

Pearl by Josh Malerman (Bird Box).

It's about a pig on a small farm that can seep into your mind and make you do and see terrible things. I picked it up after reading Bird Box and a few other books of his, which I enjoyed. I expected to give up on it based on the silly 80s horror movie premise, but the book is truly demented and creepy and I felt existentially weird after reading it

Infinite Jest - just the part about video conferencing is wild and is even mire wild when you realize it was written in the 90’s before video conferencing really existed:

“Good old traditional audio-only phone conversations allowed you to presume that the person on the other end was paying complete attention to you while also permitting you not to have to pay anything even close to complete attention to her. A traditional aural-only conversation […] let you enter a kind of highway-hypnotic semi-attentive fugue: while conversing, you could look around the room, doodle, fine-groom, peel tiny bits of dead skin away from your cuticles, compose phone-pad haiku, stir things on the stove; you could even carry on a whole separate additional sign-language-and-exaggerated-facial-expression type of conversation with people right there in the room with you, all while seeming to be right there attending closely to the voice on the phone. And yet — and this was the retrospectively marvelous part — even as you were dividing your attention between the phone call and all sorts of other idle little fuguelike activities, you were somehow never haunted by the suspicion that the person on the other end’s attention might be similarly divided.”

NOFX: The Hepatitis Bathtub. Wildest because it’s an autobiography, and they spill it all.
Edit: find the audiobook if you can

Currently reading The Illuminatus trilogy. It is a trippy, psychedelic thriller, which assumes many conspiracy theories, both well-known and obscure to be true.

Wild Animus

It's about a Berkeley graduate who takes a bunch of acid and then dresses up like a mountain Ram in Alaska and becomes increasingly more deranged.

It was on a reading list for a college class. Pirate the book if you decide to read, because the author is a raging asshole.

Dhalgren by Samuel Delany

(Close race with House of Leaves, but ultimately House of Leaves was telling a specific story, whereas Dhalgren is a semi-incoherent drug trip. Loved both books, though.)

The Metamorphosis of a Prime Intellect.

In elementary school I read this book called "Flawed Dogs" and it was unforgettably wild. It's about a dog who escapes some kinda confinement by jumping over a barbed wire fence and loses his back legs in the process, and then joins a dog gang and does dog gang activities. Also one of the dog gang members was a cat in disguise.
Honestly I should see if I can find a copy of it and reread it. It was pretty wild.

edit: I looked it up and maybe I have a lot of the details wrong but it's still pretty wild

Chuck Palahniuk's Haunted is the first thing which popped into my head.

It's a 'diegetic' anthology, the context is reminiscent of Sartre's No Exit in many ways, but taken to Palahniuk's particular style of extreme.

There's one short story in it which caused furor back in the day, but I honestly found the meta-context to be even more philosophically gruesome.

Edit: may be biased, I got the book as a gift from a girl I used to like a lot, but she... well, let's just say she was living that book at the time.

I don't know about wild, but UNSONG has been a very weird trip. It's like science fiction, except instead of science its Jewish kabbalah. There's angels, demons, alt history American politics, religious references that are truly esoteric, and puns... lots and lots of puns.

Probably some short story I read in high school but from what I can remember the first one that came to mind is Blood Meridian

Santa Steps Out was wild.

'Sex, Death, and Santa Claus

His generosity is legendary. He has a devoted wife, a crack team of sky-borne reindeer, hordes of industrious elves, and the love of good little boys and girls around the globe. But what unholy desires now propel him into the lascivious clutches of a certain fairy? And who was he before the sleigh and workshop, in times forgotten?

She munches on molars, summons drowned sailors to her pleasure, and recalls, sharp as a pinprick, her life as the most savage of ash nymphs. Why then is she stuck, night after night, hovering above pillows to leave coins for gap-toothed brats? More important, how quickly can she captivate the jolly old elf to the north?

He's huge, fluffy, lonesome, and unbearably horny. On his Easter rounds, he contrives, as often as possible, to get a grip on himself and peer into interesting bedrooms. But who in the world will throw him down and ravage him as the lovers under his gaze ravage one another?

Deadite Press is proud to bring back the ultimate erotic Christmas story from Robert Devereaux'

Gary Jennings' Aztec. Come for the historical accuracy of pre-columbian exchange Central America, stay for the depressing twisted sickening outlook.

Fanged Noumena by Nick Land

Cyclonopedia by Reza Negarestani

Both are a naked lunch level mindfuck. Don't treat it as a book, but rather as a stream of consciousness on the acid trip. Don't try to make any sense, just ride the wave.

"The teachings of Don Juan" by Carlos Castaneda. Read it in highschool and it put me off psychedelics for more than two decades.