One of the most important moments in "The Fault in our Stars" takes place at the Anne Frank House. In John Green's best-selling young adult novel, cancer-stricken teenagers Hazel and Gus take a trip to Amsterdam. While there, they make a stop at the historic landmark, where the story makes a parallel between Hazel's suffering from cancer and the terrors of the Holocaust. Hazel is very frail, but she still ascends numerous stairs (the house doesn't have an elevator), and when she wobbles into the attic, Gus kisses her to cheers from a smattering of tourists.

When it came to adapting the movie, director Josh Boone knew the scene would serve as a crucial emotional checkpoint. "It was a long involved process," Boone tells Variety. Even though no feature film had ever shot at the house, Boone knew he needed to get inside. "We wrote so many letters. Phone calls were made. For us, there was no movie without it."

On a morning last October, the keepers of the museum (who were fans of Green's novel) allowed a film crew two hours of access in the house's first-floor entrance and outside entranceway. That's how the movie shows Shailene Woodley (Hazel) and Ansel Elgort (Gus) walking up to the popular tourist destination, unsure if they should venture further.

But since the actors weren't allowed to film in the house's creaky stairways and upstairs rooms, those scenes had to be completed before the visit. To help recreate the house, Boone turned to his production designer Molly Hughes. The $12 million Fox drama had just a $90,000 art direction budget, most of which was devoted to recreating the house.

Hughes and her team built three different studio sets in Pittsburgh, one for each floor. Hughes (who worked on multiple "Harry Potter" films) had never been to the house before, but she studied photographs that had been uploaded to Tumblr. She also hired a local architect to visit the house at 6 a.m. with a handheld camera, where he was allowed to film for a single hour. He retraced Hazel's journey through the claustrophobic space where the Frank family hid from the Nazis for two years starting in 1940.

Based on that footage, Hughes meticulously went about designing the interior of the house, paying special attention to its light switches, exit signs, narrow staircases and wooden bookshelves. "My art director Greg Weimerskirch and I watched it probably 100 times, pausing on details," Hughes recalls. Another touch of inspiration came when the house cooperated by sending sample placards (which explain to tourists what they are seeing) and a patch of white wallpaper from one of the rooms. Hughes had the white pattern scanned and replicated. When she finally scouted the house, after the sets were already built, she was relieved at how much they got right.

Hughes explains that some dramatic liberties had to be taken. In the real Anne Frank House, visitors aren't allowed to set foot in Frank's upstairs bedroom. In the movie, Hazel and Gus walk right in, where they share a passionate kiss. "We talked about it at length and felt the attic was important, so we had her go into the attic," Hughes says. While this is happening, a voiceover plays in the background, reading excerpts from Frank's diary, which is meant as noise in Hazel's head.

Boone admits he was never worried that the montage would backfire with audiences. "I didn't think at all it would offend anyone," he says. "I was so not offended when I read the scene in the book. I hoped it would carry over and feel the same way."

A spokesperson from the Anne Frank House said they would be answering questions about the film later this week.

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