There are scads of low-budget movies on Netflix, but that’s no indication of quality. Sure, you can find plenty of awful B-movies and amateur debuts, but there are also plenty of gems. Take, for example, The Florida Project, a critically acclaimed indie film with an ending shot on an iPhone. Good low-budget sci-fi films are a bit harder to find, but this 2017 thriller delivers what it promises and more.

At first glance, Time Trap looks like a cheap knockoff of The Descent. Just like The Descent, it starts with a strange, cold open and then introduces the main characters as they prepare for a cave exploration adventure. But while the cave in The Descent contained merely nothing but monsters, the cave in Time Trap holds something far more terrifying.

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The film opens with Professor Hopper, played by Andrew Wilson (elder brother to Owen and Luke), as he explores the mouth of a cave, seeing a mysterious figure that looks to be … not of this time. He then ventures in further, encountering what looks like an ethereal wall.

After Hopper goes missing, his grad students Taylor and Jackie decide to go into the cave he was researching, bringing along their friend, Cara, along with her kid sister, Veeves, and Veeves’ best friend, Furby. As everyone except for Furby rappels down into the cave, they realize something is up with the way the Sun looks.

Suddenly, they realize: time moves slower inside the cave. So while they’ve been down below the surface for only an hour, whole weeks have passed by for everyone else. What follows incorporates many different legends, from the search for the Fountain of Youth to the Islamic legend of the Seven Sleepers. There’s action, there’s intrigue, and there’s actually some decent-looking special effects.

Often in time travel movies that use time dilation, it can be difficult to understand the complex quantum theory behind it. Time Trap doesn’t bother explaining its premise, and because of this, it’s much easier to buy into sci-fi. Why does time run slower in the cave? It doesn’t matter; they just have to get out.

Eventually, they discover they’re not alone, and visitors from the far off future clash with people who have been in the cave for thousands of years — at least, thousands of years above the surface. It all seems quite hopeless. After all, it’s not the kind of time travel where it’s easy to return to the way things were, but the ambitious storyline pays itself off with an ending that does feel rushed, but that’s just because of the time dilation.

Time Trap is the perfect indie gem to see storytelling in its most simple form. The exposition takes a found-footage angle, making it feel all the more real, even when the footage is found in the suit of an 8-foot-tall spaceman. Yes, it’s cheesy, but it strikes the perfect balance of mindless fun and thought-provoking concepts.

Time Trap is now streaming on Netflix.

Correction: An earlier version of this article mistakenly stated that The Florida Project was filmed entirely an iPhone, rather than just the final scene. We regret the error. Thanks Kyle!