Since a couple of weeks before Halloween I have been trawling for a real scare. Like many people, I've found my sensitivity to horror has been dulled with age and repeated exposure. Even things which used to scare me no longer work. The piecemeal measures I once used to get my spooky-fix online — combing through rambling accounts of sleep paralysis or surprising gifs — were utterly without effect.
I had never heard of Algernon Blackwood before. I stumbled across his name and the title of his incredible, entirely terrifying novella, The Willows (full text), while reading a discussion of Lovecraft's fictional influences. Lovecraft apparently considered The Willows the defining work of his genre, which he termed "weird fiction."
The craft of the story is as uncanny as the topic. Just, read it, and leave the lights on. I can't believe someone dreamed this up in 1907. I can't even describe the topic. Insofar as it informed Lovecraft's writing, it pretty much informs the modern horror genre, specifically film.