“It’s very rare you’ll be on a project,” Barrie Gower says in the latest Inside Game of Thrones video posted to Youtube, “where you’ll be decapitating somebody the one week, and then you’ll be doing a full body prosthetic the next week.” Gower says he’s been training to create characters like the Franken-Mountain since he was a boy, when he’d put latex on his face in his childhood bedroom, trying to come up with monster designs.

The set of Game of Thrones looks like a dreamscape for Gower and his team, whom the video follows as they sculpt and airbrush the White Walkers and painstakingly stitch individual hairs onto silicon heads. Gower says the timetable for creating a prosthetic character from scratch is “about four weeks”. The de-rigging process, which takes place at the end of a shoot, is carried out with meticulous care, because, as Gower mentions, ripping a prosthetic off would take the first layer of an actor’s skin with it.

It should come as no surprise that filming the battle at Hardhome was Gower’s favorite Game of Thrones memory, as the scenes were filled with his icy-looking White Walker faces and bodies. “We were covering them in loads of rubber each day. At times, it felt like pandemonium, and then you’d look across and have a look at the monitor, and it was so cleverly choreographed and orchestrated. […] The feeling of achievement was incredible.”

Watch the entire featurette below.