Sherlock Holmes (novel)/Nightmare Fuel


 * The titular substance in The Devil's Foot is literally this. In a less literal sense, Holmes and Watson testing it on themselves.
 * The Adventure of the Copper Beeches is chock full of Nightmare Fuel. First, there's the poor governess, who is brought to a mysterious countryside manor, where she is subject to bizarre demands, discovers that her boss is a Complete Monster, and finds the child she is to care for takes a perverse delight in torturing animals. Likewise for Rucastle's daughter, who has been imprisoned by her unstable father for some time to keep her from marrying and obtaining her inheritance. This would be creepy enough, but the setting of the story means that the two girls are entirely at the mercy of an unbalanced sociopath, and can draw on no one for aid. (Holmes even comments that the isolated country setting can elevate ordinary crimes to the level of Nightmare Fuel.) Also, depending on your feelings about dogs, the vicious, half-starved mastiff can count, too.
 * The Speckled Band, especially if you don't like snakes.
 * "The Creeping Man" is, well, super creepy.
 * The titular hound in Hound of the Baskervilles. Even though it turns out not to be supernatural, it's still huge and vicious and glowing.
 * The hydraulic press in 'The Adventure of the Engineer's Thumb', it being the reason the engineer of the title is missing said digit.