In The Luminous Dead, Caitlin Starling decided to take on a challenge by building an entire story with two characters and a cave. And it did not disappoint.
On Gyre's planet, the fastest way to make money is to work as a caver, mapping caves and finding mineral deposits deep below the surface. But the caves are perilous, full of steep drops, flooded passages, and the Tunnelers. These worm-like monsters seem to swim through solid rock, causing earthquakes and cave-ins. The only way to send cavers down without attracting a Tunneler is to send someone in alone, encased in a high-tech closed environment suit.
If Gyre does one assignment and survives, she'll have enough money to get off world for good. So she fakes her credentials and successfully gets hired on as a caver. But once she's in the cave she's completely alone. Her only company is Em, a voice in her ear, the handler who is watching Gyre's suit readouts safely on the surface.
As Gyre navigates the cave, she finds the bodies of previous cavers, discovers her handler is lying to her, and is accidentally exposed to spores from bioluminescent cave fungus. Then Gyre starts to feel like she's being watched...
While I love science fiction, I don't typically read horror. Really, I shouldn't be allowed to, since I don't deal with it well. And I know not to read books about dark caves after the sun has gone down, but I did it anyway. Starling's descriptions of the cave were enough to unnerve me even before Gyre starts to worry that she's not alone in the darkness. By then, I was fully invested, face inches away from the text during tense scenes.
Obviously, not everyone will be as unsettled by The Luminous Dead as I was. But regardless of your ability to handle scary stories, Caitlin Starling has a gripping and easy to read writing style. I definitely recommend it if you're interested in a slow build, psychological horror.