Having been through seven increasingly audacious seasons of HBO flagship series Game of Thrones, visual effects producer Steve Kullback always looks at a new season from the same perspective: “Geez, how the hell am I going to do this?” Working with “no-holds-barred” creatives David Benioff and D.B. Weiss, along with VFX supervisor Joe Bauer, the collaborators always tend to come to the same conclusion about the road ahead: “Well, that’s amazing, but obviously it’s unproducible.” And yet the innovative Game of Thrones team forges ahead.

With each new season, Kullback and Bauer have seen the volume and complexity of their work double—even as the episode count per season continues to shrink. “Steve’s line is that the work doubles in relation to the size of the dragons, who also double in size from season to season, up until Season 7,” Bauer explains.

In Season 7, as it happens, Dany’s dragons are out in full fire-breathing force, wreaking havoc on the people of Westeros. Also present this season are zombie polar bears, major action sequences on the seas, and a harrowing confrontation between Jon Snow and the Night King on a frozen lake.

But perhaps most remarkable of all—and most significant in its implications for the series’ final season—is that final moment in The Dragon and the Wolf, when a zombie dragon brings The Wall down. It was only through the combination of real photography shot in Iceland, digital modeling and complex simulations that Kullback and Bauer were able to bring this transformative moment to fruition.

After seasons of heavy anticipation, Dany’s dragons are finally front and center this season. What has the process been in bringing the dragons and their fire-breathing sequences to life?

Bauer: The first thing we do is we make a pre-viz, a cartoon of the coverage of the episode. We go to the locations where we’re shooting, and we make digital models of those locations by various means, and then we block it out based either on storyboards or in consultation with the directors, bringing all the information we know at that point together, and then visually telling the story, largely without regard to how we’re going to do it. Just kind of making “the wish movie.”

Then, we start breaking it down into pieces. What that ends up being on set is either a camera flying over on a cable rig that everybody knows is supposed to be the dragon or a parking cone high on a rock somewhere. When we get to stage, it can be a 15-foot pole with a ball on the top—or we’ve laser cut part of the head of the dragon, or most of the face, and put that on a pole. This year, those are the techniques. It’s whatever method gets the eye-lines to be correct, basically.

Kullback: Once upon a time in Season 3, when we were shooting in Split [Croatia] in Diocletian’s Palace, which played for dragon daycare, Dany was luring the dragons down below. The camera was following Joe and myself puppeteering one-to-one sized dragon heads, which were laser cut. Now, we have some pretty sophisticated tools for real-time positional motion tracking with Ncam, to be able to use the pre-viz models. Sometimes, the more fully animated dragon performance is integrated into a scene, so that the operators can actually follow the performance, regardless of where the camera’s placed.

One of the things that Joe has brought to the table, that is probably our secret weapon, is that we shoot an enormous amount of photography—of organic, very real elements. Going back to Season 5, when Dany’s rescued in the fighting pit, we talked about how to proceed with fire, now that we’re big, badass dragons breathing fire and taking people out. Joe said, “Obviously, what we need to do is pre-animate the dragons and apply the animation to a motion control crane, put a flamethrower on it, and blast the [scenery] for real.

Bauer: And they didn’t fire me on the spot. [laughs]

Kullback: Our producer, Bernie [Caulfield], her first words were probably, “Are you out of your f*cking mind?” We asked Panavision if they’d be okay putting a flamethrower on a technodolly and they thought, “Yeah, that’d be cool.” Then, we moved on to the special effects and stunt folks. It turned out to be not only the best quality image but also much safer because the performance of the fire was robotic. The stunt folks knew exactly where to hit their marks, and exactly when it was going to hit them, and how. Everybody initially was scared to death, including us, but in the end…

Bauer: It removed variables. That’s sort of a general statement about working on the show. Because of how quickly we have to turn it around, we need to minimize how much work we have in post. The more that we can take care of in the shoot, the faster the show comes together, and the better it looks.

Bearing in mind that so much of the show is shot practically, what’s required of you when it comes to the series’ complex battle sequences? This season, several of those sequences are on the seas.

Bauer: We make the “wish cartoon” of what it ought to look like when it’s all finished, we dig in and see what out of every shot we’re able to shoot for real, and then, we know the rest of it has to be added digitally. There’s one fully built boat that we shoot on, and that becomes all boats of all designs, pretty much—although The Silence was another design.

Then we know that we’re making all of the surrounding boats, all the water, the atmospherics, the weapons. We shoot a lot of fire elements, particularly. In a battle, we’ll frequently tile, so we’ll do the hero action closest to camera, but then we work out by measurement, moving all of the extras several times and shooting again, to help us fill out the army. Then we’ve got a chunk of it that’s photographed, and we fill it out the rest of the way digitally.

Kullback: For the Spoils of War episode, it was basically cowboys, Indians, and fire-breathing dragons. Everything in the environment was pretty much there, with the exception of these rather spectacular views…

Bauer: …Like Monument Valley. There was a line in the script the boys wrote that said it was a John Ford vista, and Matt Shakman, the director, couldn’t have been more literal with that. You do get into augmenting the environment, generally making it bigger and wider.

So there is a fair amount of set extension and worldbuilding to augment the series’ sets, which already have their own huge scope?

Bauer: Yeah. Sometimes you go to the location, rather than try to make it. But more and more, it seems like we’re making it because you can’t really shoot in snow very long. They shot a lot in snow in Season 7, with the group on the move through these big Icelandic locations, but they really were beat to death by the weather, and also the days were quite short.

The frozen lake, which was Episode 6 of Season 7, was a big concrete rock quarry that was dressed up to about 25 feet in snow and ice. Then, we flew a helicopter over a bunch of mountains in Iceland and made digital models of them that are photographically real, and planted those on top of the rock quarry in all directions. We were combining two locations together, using that method, and it worked really well. When we lay these environments out, we make digital models from photogrammetry, which is sort of a LiDAR technique, but then we bunch them all together into what the mythical world is.

The most stunning moment in Season 7 would have to be the collapse of The Wall. What went into that season-capping moment?

Bauer: That’s Iceland again, for the most part. We were on this black volcanic beach, scouting. Right on the coast, there was a sleet storm, and the ice was coming down so hard that if you looked into it, it would have gone through your face. It was really something else. There are these big volcanic cliffs that are several hundred feet high, and jut out into the ocean. There happened to be a lighthouse and we said, “If we say that the lighthouse is the Eastwatch castle, then the helicopter pilots can cue off of that.”

Again, we did our helicopter flyover and made a digital model of that whole beach area, and then we built the CG ice wall to incorporate that—and the ice wall extends about a quarter mile out into the ocean. Then we worked out all of these flight plans for helicopter photography, based on where the lighthouse is. The pilot was so good that when we got the plates back, we stuck the CG ice wall in, and everything was perfect. It really was some masterful flying.

Basically, what we did was work with real ocean, real environment. We did have to snow it up because it wasn’t very snowy, and then added the digital ice wall, and then extended things. The trees, you had to fly somewhere else for, because there aren’t a lot of trees in Iceland. Then we changed a lot of the skies, as we usually do. But that was it for the environment.

Then, collapsing it was just a very complex digital simulation by the vendor. When one of the dragons breathes fire, we have a company called Spidercam, and generally, they fly cameras around sets—Mission Impossible and all of these. But we’re the first ones to put a flamethrower on their rig. We have a gigantic stage, we put the fire on that, and fly it all around the stage. That’s what we use for our elements for the dragon fire. So we built this big metal wall and just blasted away at it. We shoot the dragon fire off of a motion-controlled wire rig. The ice dragon, Viserion, that’s what his fire was. The rest of it is a digital simulation. Then, we had to take over the water as well, so the wall falling into the ocean would behave properly.

Can we expect an even greater level of ambition as we head into Game of Thrones’ final season?

Kullback: I don’t think it would come as a surprise or be a betrayal to the production to tell you that it is many times bigger and more badass than anything we’ve done before, and probably anything that’s ever been put together for the smaller screen.

Bauer: I think we’re all going to be extremely proud when we get to the other end of it.

Kullback: We have so many more people to kill this year.