Spelunking is nightmare fuel for me. Tight spaces, pure darkness and creepy crawlies that never see the light of day. It might not be the usual fare for horror flicks, but it's the setting for one of my favorite horror movies of all time.

When a group of friends goes exploring a local cave system, they're prepared for the claustrophobia of tons of rock pressing down around them, but not for the devilish monsters hiding within dark tunnels. 

The Descent is a 2006 horror flick you can watch for free with a Prime Video subscription. A cult classic infused with hints of terror in every frame, this movie has struck fear into the hearts of audiences for nearly 20 years. 

I've been a fan of horror movies since the 1980s, starting with classics like Pumpkinhead. Over time, I've found some that I keep coming back to, even when I know how they're going to end. The Descent is absolutely one of them.

The Descent delivers a claustrophobic, dread-filled experience. If you don't like tight spaces, it's even worse. Every time I watch, the deadly disaster has me covering my eyes and screaming as events spiral out of control. 

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The movie starts at the conclusion of a whitewater rafting trip, where six women have been bonding and having a great time. On the drive home, the lead character, Sarah, loses her husband and their daughter in a car accident that shatters her world. That tragedy sets the tone for the entire movie, warning viewers that things are only going to get worse. 

What starts as a fun friends' adventure quickly dissolves into madness and terror.

Celador Films / Pathé Distribution 

A year after the deadly car crash, the six friends reunite for another adventure. Their plan is to spend a day spelunking in a North Carolina cave system in the Appalachian Mountains. Things start off fine, but then Sarah becomes stuck in a particularly narrow passage. She manages to squirm through, but a rockfall behind her leaves all of the women trapped deep underground with no idea how to get out. 

One of the friends, Juno, then admits that they're not in the exact cave system she'd reported to local authorities, but instead in a never-before-explored section. They're entirely on their own, with no hope of help. 

As the women progress deeper into the cave, looking for an exit, they find old climbing equipment along with a painting that might point toward a way out. Another member of the group, Holly, rushes forward at a sign of light, before falling into a hole and breaking her leg. While the other women tend to her, Sarah looks around and sees a creature drinking from a pool of water before it notices her and scurries into the darkness. 

The "Crawlers" in The Descent are terrifying creatures who live in the dark spaces.

Celador Films / Pathé Distribution

After that, things go from very bad to much, much worse. The women encounter a large room filled with animal bones and the creatures that fed on them. These pale humanoid monsters, which the women dub "Crawlers," attack them viciously in the dark while they fight back as best they can.

Holly, hindered by her broken leg, is the Crawlers' first victim, and she's quickly dragged off into the darkness. In the ensuing chaos, Sarah is knocked unconscious, while Juno accidentally stabs friend Beth in the neck. June flees, but not before Beth snatches a pendant around her neck. 

When Sarah regains consciousness, she sees a horrifying sight. Crawlers fight over her friend's body and realize the utter bleakness of the situation. Sarah refuses to give up, though, and buckles down for a fight, prepared to find her way back to the surface. 

I won't spoil the devastating third act. You'll need to watch yourself to learn whether Juno and Sarah survive the horrors of the tunnels and the Crawlers that inhabit them. At just under 100 minutes, this dark plunge into terror works great as part of a movie marathon or a quick weeknight flick. 

The Descent has thrilled audiences for two decades and quickly reached classic status for a good reason -- it's a tightly paced and very scary movie that drags you deep under the earth, delivering a story and characters you won't forget. Stream it now on Prime Video to discover all of the terrors that the caves are hiding.