The Upside Down, a parallel dimension accessible through the sleepy town of Hawkins, Indiana, is a haunting campfire story come to life. When Netflix's Stranger Things became the surprise summer breakout of 2016, fans glommed onto the moody, atmospheric netherworld, and the truly terrifying monsters that poured from it to terrorize Hawkins' human residents.

Season 2 only upped the ante, creating a huge challenge for Production Designer Chris Trujillo, and the VFX (Visual Effects) team of Christina and Paul Graff. They had to bump up the scale, while not giving away the full mythology (Seasons 3 and 4 are reportedly coming down the pike).

"We started brainstorming with what we thought was visually successful about Season 1. Which, for me, it's all the sort of gloom and the environment and the general sense that things are like wet and sick," says Trujillo. "We essentially started from the same aesthetic ideas and then just were able to get even bigger."

Touching on what made Season 1 so successful is what helped Season 2 retain that quality of living in a child's nightmare — complete with a child's understanding of one. Using that ethos as a touchstone, the team managed to take the Upside Down to cinematic levels without losing what made it so scary and gripping in the first place. What Trujillo and the Graffs ended up with are some of the most unsettling visuals in the history of the small screen.

The Mind Flayer

The Duffers, creators and co-showrunners of the series, wanted this season's big bad to feel larger than life, almost like a force of nature. They ended up with the Mind Flayer, a giant sentient spider-esque creature that eclipsed even the largest buildings in Hawkins.

"My instinct was just to find bizarre, interesting, real things and figure out how to build from that," says Trujillo. "So my actual initial inspiration when we started designing that, the storm and the Mind Flayer [for the arcade scene] was this incredible phenomenon where lightning storms occur as a volcano is erupting, and it's f--king mind blowing."

The Graffs were brought in to give Trujillo's creature a real sense of scale. Nailing the look of the Mind Flayer was one of the first visual aesthetics they finalized, but the process was a long one. "We did some research based on what the Duffers and Chris gave us and we figured it's gonna be something between a tornado and an electric phenomenon," says Paul Graff. "But it's not like you get it right the first time, it's like you work on it and you look at it and try to figure out...how can we make it look better and you change it and then you ask the same question and do that until you really feel like this is as good as we can do."

Ultimately what they created was, "a creature that visually felt like this sort of physical manifestation of the mood of the Upside Down."

Will's Visions

Once the team locked the visual aspect of ominous Season 2 threat, it was time to figure out how they'd graft the horror of the Mind Flayer over Hawkins. In Season 1, we were introduced to Will Byers (Noah Schnapp) a boy lost in the Upside Down, who returned at the end of the season...not quite right. Picking up in Season 2, The Duffers had written in flashes — from Will's perspective — into the Upside Down, visions he experiences as he tries to live the life of a normal preteen boy in a suburban town. Early on it seems like the flashes might be a result of PSTD from Will's Season 1 kidnapping, but the Mind Flayer stalks closer in every flash. It soon becomes clear that the Upside Down is reaching into the real world through Will's mind.

"There's a few instances where we're in really big worlds this season. Basically anytime Will's seeing the Upside Down like, the arcade scene, the trick-or-treat scene or the porch scene," says Trujillo. "[And that requires] everything onscreen [to] originate in something physical." The challenge in Season 2 was grounding the massive scale of Will's visions in something real on camera. Season 1 was significantly simpler in this regard because most of the effects were practical, and done on set. But in Season 2, because the audience's view of the Upside Down was growing, so were the amount of digital effects used in each big scene. Trujillo's job was to anchor the whole scene on set, and give the Graffs something eerie enough that they could marry it to the Upside Down.

"The Byers house for example, is on stage complete with the front porch and a backdrop. So a shot like that, we completely dress out the whole porch and the ceiling and the floor," says Trujillo. By dress out, Trujillo means his team physically redecorated the outside of the Byers house to look like it was in the Upside Down. This included weathering, the breathable substance they use as dust motes, and generally anything Trujillo felt would add a sickly look. He exhausted "all physical, practical material" before the Graffs took over, using VFX "to extend the larger vista, because essentially, VFX came in to make it feel a little realer." Everything the audience sees over Will's shoulder and in the sky as the Mind Flayer looms is the Graffs.

"We had such a big show this year and a tight schedule we did the Upside Down basically as a digital set dressing," says Christina Graff. That overwhelming scale was only achievable for the VFX team because once they had solved the visual language of the Upside Down, they could easily adapt it to other scenes.

"The most challenging sequence we had, just because it was so big so there were actually two in play, was Hawkins Middle School, the interior school and exterior school when Will runs through the hallway and he runs outside, we have the Mind Flayer invading his space, his orifices," says Christina Graff. "Nothing was done practically. It was all done digitally, so in order to perfect that specific scene we had to perfect the scene before that which was what we call the trick-or-treat sequence [where Will flickers into the Upside Down while trick-or-treating, and hides from the Mind Flayer beneath a neighbor's basement stairs]."

The trick-or-treat sequence is the first time the Mind Flayer attempts to touch Will, the eerie tendrils of smoke and black particulate surround him as if looking for a way to crawl into him — exactly what happens in the scene at Hawkins Middle School. The creepy crawly movement of the first scene set up the second, where Will is finally consumed by the Mind Flayer as it fill up every space around and within Will.

Dart and the Demodogs

The Mind Flayer wasn't the only creature the team had to crack this season, and ironically the smaller fish (well, demons) were harder to fry. Conceptualizing Dart, a stray pet Dustin (Gaten Matarazzo) takes in without realizing it would grow into a full-fledged monster, was a significantly more arduous task. "The Duffers knew they wanted to create something that is endearing and cute and small for Dart," says Christina Graff. "Cute in the Gremlins sort of way," adds Trujillo. "We wanted this creature that seems sort of sweet and innocuous to then slowly reveals its monstrous side."

The team reverse-engineered Dart: "We had to think about the Demogorgon [Season 1's big bad] as a creature that goes through stages and develops over time and molts and all that — basically working backwards from the Demogorgon in Season 1 and figuring out what stages of the evolution in the life cycle of a Demogorgon would look like," says Trujillo.

The Duffers knew they wanted three to four stages, from a baby to an adolescent Demogorgon. So the Graffs started with a "frogogorgon", the tadpole sized monster Dustin first discovers in his trash towards the beginning of the season. The next stage they called a "catagorgon", which, ironically, is the size big enough to eat Dustin's cat. And the last stage was originally called a "dogogorgon", then flipped to demodog in the script. "He needs to be big enough to sit in the Ghostbusters pack," Trujillo notes. "But then we need him to be big enough to eat a cat and be really scary, you know what I mean? So it was figuring out the physical size elements first."

"And at what point does his face open up? Because clearly, it starts out and you can't quite tell that it has this monster maw," Trujillo continues. "In order to not give it away that it's actually a Demogorgon, we had to be careful about making sure that its tether mouth isn't obvious, and it didn't even have four legs in the earlier stages," adds Christina Graff.

The Tunnels

Midway through the season, the heroic Chief Hopper (David Harbour) is poisoned by some flora and collapses in tunnels underneath Hawkins that connect the town and the Upside Down. The same tunnels later serve as the locale for a showdown between the demodog pack, Dart and our heroes. The fabrication of these scenes was Trujillo's biggest triumph of the season.

"It was a 'as above so below' kind of a thing where the sickly vines in the first episode were mirrored by the tunnels which are a larger manifestation of the vines. They're the vehicle by which the Upside Down colonizes our world," says Trujillo.

Almost all of the vines, from the central chamber/gate to the Upside Down, to nearly every junction and tunnel, were built practically. That ended up encompassing thousands of square feet of tunnels, an incredibly elaborate architectural challenge. "We ended up creating these systems of differently sized rings that we offset" Trujillo continues. "You have to build this incredible, weird, organic space out of these raw, geometric materials."

"The tunnels are in the real world but they're basically an organism by itself. They aren't made out of earth, they have a skinny exterior because it's literally like a creature itself," adds Paul Graff.

The Graffs were more concerned about what appeared in the tunnels; namely the flora. "There's vines, there's nether stretch [prehensile vines that grab the characters], there's nether flats [stationary vines] and there's nether clusters [a flower that sprays Hopper] and the spores," says Paul Graff. The Graffs designed effects for all the flora with third party vendors and layered them over the scene until the final result was an eerie graveyard, one that threatened the real scope of how far the Upside Down could spread.

The Gate in Hawkins Lab

Unequivocally the most terrifying display of power — and VFX — this season was the scene in which Eleven (Millie Bobby Brown), a young girl with telekenetic powers, and Chief Hopper head deep within Hawkins Lab to the site of the gate. The gate might imply a simple entryway, but when Eleven and Hopper drop into the initially seemingly empty space, it was clear that they were dealing with a thin membrane separating the two worlds.

"The whole final sequence in the lift chamber, when Eleven closes the gate [was hardest to conceptualize]," says Paul Graff. "Because basically what you have there is a cage suspended in a studio on a soundstage with three panels of blue screen on rollers around it."

"Everything else is just in our heads and we have to get it into Millie's head and then David's head," continues Christina Graf. "The key to that scene was really advanced storyboards. Literally if you go to the storyboards of the scene it's almost one to one of what you see at the end in 'Chapter Nine'."

The Graffs spent a lot of time at the proverbial and literal drawing board for this scene. Once they got the script, they tried to figure out how many shots there would be in conversations with Trujillo and the DP (Director of Photogrpahy). Once they had a sense of what the camera would be looking at, they began concept designing, which weren't finalized until third party vendors could nail the specific details of the effects need to literally paint in 80-90 percent of the scene. Where the tunnels were all practical, most of this scene existed inside a computer.

The Snow Ball: Last Shot of The Season

The very last shot of the season is the only one in which the audience sees the Mind Flayer through their own viewpoint, instead of a specific character's. It takes the joyous energy of the Snow Ball, a middle school dance, and rotates 180 degrees through the ground to reveal the Mind Flayer looming over the school in the Upside Down. The ominous shot was one of the crew's favorites, and all happened thanks to Paul Graff.

"We sent the Duffers this concept because [in the script] it says there's a turn and we see the monster over the school," Graff recalls. "So we figured, well, what if we do actually turn the camera physically upside down to get there? We decided we're going to go through the ground and come back up to the Upside Down.

"But it was really hard to shoot because...You're on a really, really tight schedule at the end so you don't have any time to mess this up," adds Christina Graff. And that particular day on set, the camera operator didn't have the right equipment to keep the camera attached to the crane if the crew flipped the shot the way the Graffs has planned. "It was like a little bit of a mind game of how this all fits together. In order to keep the shot level and actually work for post, we had three camera operators operating each wheel of the control head, and it was a real ball buster," says Paul Graff.

"I think it was like fifteen takes but we finally got it right and it looks really cool. Totally worth it," says Christina Graff.

Season 3

Bringing all these elements together was no small task, but Trujillo and company executed flawessly. And they're not quite done yet.

While neither Trujillo or the Graffs wanted to get into too many details, all three confirmed they're sitting on a massive stack of unused ideas for Season 3.

"This whole year came and all of these challenges and it was really invent it as you go, right?," says Christina Graff. "At the very end when I was cleaning up my desk I found these cards and I'm looking back at these cards from the very beginning of the show and I realized, you know what...half of what's on those cards we did and half of it we didn't, and we did other things instead. So what's just on the cards that never made it in the show is more awesome than anything else I've seen on any other show — so I think there's gonna be a lot of cool ideas coming up."

Trujillo agrees, saying, "There's definitely some research we did in the process of figuring out elements of the Upside Down, some really interesting, weird ... we were looking into a lot of amphibious egg sacs and stuff. There's definitely some interesting ideas for other flora and fauna that we haven't yet been able to kind of get our hands around. There's endless potential for making scary, gross stuff for the Upside Down."

No matter what the team comes up with, fans can count on one thing: they'll need a loyal group friends by their side to brave the horrors ahead. Whatever oozes up from the Upside Down in Season 3, it'll be sure haunt everyone's dreams.

Stranger Things Season 2 is now streaming on Netflix.