Warning: This article will have spoilers from the latest episode of Game of Thrones.

Last week, fans of George R.R. Martin's A Song of Ice and Fire series and non-book readers alike were delighted by the impressive sequence at the end of the Game of Thrones episode "Hardhome," which featured the Wildlings, a few men of the Night's Watch, and a giant named Wun Wun facing off against the White Walkers and their army of undead wights.

As book readers know, the devastation beyond the wall originally happened off-screen. The showrunners gave viewers the opportunity to see the action by bringing Jon Snow and Tormund right into the thick of it. "This was an opportunity to show the audience something that is going to be fresh for everyone, whether you're a book reader or not a book reader," David Benioff said. 

HBO just released this fantastic video that breaks down how the show's team created the scene, which required building a real wall and outfitting hundreds of extras in prosthetic makeup. "Those White Walkers actually looked like that on set!" Kit Harrington told Vulture. "With the eyes and everything. That's all prosthetic. It's not CGI at all." The creators walk through the decisions they made to fully capture the horror of the massacre, which lasted 20 on-screen minutes but reportedly took a month to film.