Horror rooted in the fear of humanity's insignificance before vast, incomprehensible, and indifferent cosmic forces.
Cosmic horror doesn't scare you with monsters. It scares you with scale. The universe is vast, ancient, and utterly indifferent to human existence. The entities that inhabit it aren't evil; they're beyond morality, beyond comprehension, and sometimes beyond perception. Encountering them doesn't threaten your life so much as your sanity, your sense that reality is knowable and that humanity matters at all.
Cosmic horror teaches you to write fear of the unknown, not fear of the dangerous. It's a masterclass in suggestion over explanation, and the technique of making something scarier by refusing to fully describe it transfers to any genre. Understanding it also helps you engage with Lovecraft's legacy critically, taking the useful elements while discarding the bigotry.
The genre's founding text: fragmentary knowledge of something so vast and alien that understanding it destroys the human mind.
An unknowable zone transforming everything it touches, cosmic horror through biology rather than tentacles.
If you explain exactly what the cosmic entity looks like and wants, it stops being cosmic. The horror comes from what you can't understand.
Modern cosmic horror has evolved far beyond Lovecraft. You can use his sense of scale without replicating his worldview.
Write a scene where a character discovers something that shouldn't exist: a sound, a pattern, a spatial impossibility. Don't explain it. Let the character try to understand it and fail. End the scene before they (or the reader) get answers. The discomfort of not knowing is the whole point.