Here’s a trick that’s been around for a while but may have passed you by: secret category codes added by Netflix engineers that can help you narrow down your on-demand video choices. From classic war movies to Brazilian dramas, here’s how to dig deeper into the Netflix library.

Whenever you dive into a genre on the Netflix website you get a URL that looks something like www.netflix.com/browse/genre/6839—and if you play around with that end number you can discover some hidden gems. How about visually striking films for ages 5-7? Or period pieces? We’ve found two unofficial lists online, here and here.

Not all of these codes work, which isn’t surprising given the hidden nature of the feature, the constantly shifting Netflix catalog, and the variations between countries, but a lot of them do. It’s fun turning up a few obscure films that you might not otherwise have discovered.

If you’ve got time on your hands then it’s not difficult to build up your own list of sub-genres by changing the number at the end of the given URL. If you’re interested in how Netflix organizes its content and what these categories are for, read this Atlantic article where Alexis Madrigal first happened upon them.