"The Jaunt" by Stephen King is my personal favorite short story from him. It has elements of both horror and science fiction. In it, Stephen King takes the well-known science fiction concept of teleportation and turns it into a futuristic horror story. A lot of what is the "horror" in this story is left to the imagination, but what we do know of that horror is so mind boggling that it is one of the most powerful concepts King has ever come up with.
The name of the story comes from the name teleportation is given in "The Jaunt." The story begins as a man, his wife and their two children are getting ready to teleport or "jaunt" from the Earth to Mars. The man has done this several times, but his children are new to it and so he decides to tell them the history of the jaunt. King takes the reader back to the 1980s and a fictional Earth where resources are dangerously low and starvation is spreading like an epidemic across the globe. An old, eccentric scientist is trying to develop a means of teleportation to solve all of these problems and he is successful. However, there is a problem.
When the scientist puts his test mice through his teleportation device, they come back dead or near dead. The ones that come back near death exhibit strange behavior. As the story progresses, the reader learns that the body teleports in mere seconds, but those seconds are an eternity to the mind. The problem is fixed by putting anything that is jaunting alive to sleep before teleportation, including humans. The father knows horror stories of humans coming through the jaunt awake, but he keeps the sordid details from the children, allowing only the reader to know just how horrible the jaunt truly is.
Finally, as they wait to jaunt, the attendants come around to put the family to sleep. After a few moments, the father wakes up in Mars to the sound of his wife screaming. He goes to where his wife was pointing to see his son laying there with yellowed eyes and white hair. The boy yells to his father that he faked taking the gas to sleep and that it is longer than eternity in the jaunt before screaming and tearing at his eyeballs. The father refers to the boy as an old "it" inside of his son's body. King's description of this moment has stuck with me since the first time I read it so many years ago.