Type of Media: Short Story
H.P. Lovecraft is one of the most influential horror writers of the 20th century. His Cthulhu mythos is read and recognized all over the world, not only because of his own stories but also because of the works of those who built upon his lore like August Derleth. Indeed, probably a big reason for Lovecraft's popularity is the public domain status of his work, which allows anyone to create media based on the Cthulhu mythos.
As a result, there are many people who consider themselves Lovecraft fans but who haven't read any of his stories. If you're one of these people and you're looking to dive into Lovecraft's original works, I recommend The Colour Out of Space as a good jumping off point. It contains many of Lovecraft's typical themes (a New England setting, a story within a story, people transforming into horrors) and gets you used to Lovecraft's writing style, which was considered old-fashioned even in the 1920s.
In The Colour Out of Space, a man from Boston is asking around Arkham, Mass. for information regarding a spot called "the blasted heath" that the locals won't go near. The only person who knows anything about it is an old, allegedly crazy man named Ammi Pierce, who tells the man from Boston that the land used to belong to his friend Nahum Gardner.
Nahum was a successful farmer with a big family. One night a meteor struck Nahum's land. Scientists from Boston came to test the meteor and found it had strange properties, most notably that it rapidly dissipated in air and it emitted a color that no one could identify. While the meteor was treated as a fun curiosity for a while, over the next two years it began affecting Nahum's land and warping his family's minds until the farm and the Gardners were brought to ruin.
As with most Lovecraft stories, the characters don't wind up fixing or solving any problems by the end. The Colour wreaks its havoc on the Gardner family and then seems to leave, and the surviving characters are left a little less sane and trusting of the world. Lovecraft's universe doesn't present the terror facing humanity as a fight we can win, and in the few stories where people can band together and eliminate some evil, like The Dunwich Horror, it's always after that villain has unleashed an even greater evil. Reading these stories aren't going to help you sleep at night, but they might give you a new perspective of how tiny we human are in the great scope of things.