In the late 1990s, stories about what was happening on the set of Stanley Kubrick’s already-secretive film Eyes Wide Shut constantly made headlines. Everyone wanted to know what was going on behind the scenes with real-life celebrity couple Tom Cruise and Nicole Kidman, and the 15-month shoot only intrigued people more. Finally, the film was released on July 16, 1999—more than four months after Kubrick had passed away. While there is still a lot we don’t know about the movie, here are 20 things we do.

1. THE FILM IS BASED ON A 1926 NOVELLA.

Eyes Wide Shut is loosely is based on Arthur Schnitzler’s novella Traumnovelle (Dream Story), which was published in 1926. Considering that the movie takes place in 1990s New York, it is obviously not a direct adaptation, but it overlaps in its plot and themes. “[The book] explores the sexual ambivalence of a happy marriage and tries to equate the importance of sexual dreams and might-have-beens with reality,” Kubrick explained. “The book opposes the real adventures of a husband and the fantasy adventures of his wife, and asks the question: is there a serious difference between dreaming a sexual adventure, and actually having one?”

2. PRODUCTION ON THE FILM BEGAN IN 1996.

By then, Kubrick had been holding onto the rights to Traumnovelle—which screenwriter Jay Cocks purchased on his behalf, in order to keep the project under wraps—for nearly 30 years. Kubrick had planned to begin working on the film after making 2001: A Space Odyssey, but then got the opportunity to adapt A Clockwork Orange.

3. THE STUDIO PUSHED KUBRICK TO CAST A-LIST NAMES.

Terry Semel, then-head of Warner Bros., told Kubrick, “What I would really love you to consider is a movie star in the lead role; you haven't done that since Jack Nicholson [in The Shining].”

4. KUBRICK WANTED TO CAST ALEC BALDWIN AND KIM BASINGER.

Kubrick liked the idea of casting a real-life married couple in the film, and originally considered Alec Baldwin and Kim Basinger. (He also liked the idea of Steve Martin.) Eventually, he went with Tom Cruise and Nicole Kidman, who were married from 1990 to 2001.

5. NEW YORK CITY WAS ACTUALLY LONDON.

Though the film is set in New York, it was filmed in London. In order to construct the most accurate sets possible, Vanity Fair reported that Kubrick “sent a designer to New York to measure the exact width of the streets and the distance between newspaper vending machines.”

6. SOME OF THE SHOTS REQUIRED NO SET AT ALL.

In order to give the movie a dream-like quality, the filmmakers used an old-school method of shooting—and a treadmill. “In some of the scenes, the backgrounds were rear-projection plates,” explained cinematographer Larry Smith. “Generally, when Tom’s facing the camera, the backgrounds are rear-projected; anything that shows him from a side view was done on the streets of London. We had the plates shot in New York by a second unit [that included cinematographers Patrick Turley, Malik Sayeed and Arthur Jafa]. Once the plates were sent to us, we had them force-developed and balanced to the necessary levels. We’d then go onto our street sets and shoot Tom walking on a treadmill. After setting the treadmill to a certain speed, we’d put some lighting effects on him to simulate the glow from the various storefronts that were passing by in the plates. We spent a few weeks on those shots.”

7. THE MOVIE IS A GUINNESS WORLD RECORD HOLDER.

The film has a place in the Guinness Book of World Records for the longest constant movie shoot, with a total of 400 days, which was a surprise to the cast and crew. Cruise and Kidman had only committed to six months of filming. The extended shoot was a lot to ask of Cruise in particular, who was at the height of his career. He even had to delay work on Mission: Impossible II to finish Eyes Wide Shut. He didn’t seem to mind though. “We knew from the beginning the level of commitment needed,” Cruise told TIME. “We were going to do what it took to do this picture.”

8. THE SCRIPT KEPT CHANGING.

According to Todd Field, who played Nick Nightingale (and is an Oscar-nominated filmmaker in his own right), “We’d rehearse and rehearse a scene, and it would change from hour to hour. We’d keep giving the script supervisor notes all the time, so by the end of the day the scene might be completely different. It wasn’t really improvisation, it was more like writing.”

9. CRUISE DEVELOPED ULCERS WHILE SHOOTING THE FILM.

“I didn't want to tell Stanley," Cruise told TIME. “He panicked. I wanted this to work, but you're playing with dynamite when you act. Emotions kick up. You try not to kick things up, but you go through things you can't help.”

10. CRUISE AND KIDMAN SLEPT IN THEIR CHARACTERS’ BEDROOM.

In order to reflect their real-life relationship, Cruise and Kidman were asked to choose the color for the curtains in their on-screen bedroom, where they also slept.

11. THE APARTMENT IN THE MOVIE WAS KUBRICK’S.

According to Cruise, “The apartment in the movie was the New York apartment [Stanley] and his wife Christianne lived in. He recreated it. The furniture in the house was furniture from their own home. Of course the paintings were Christianne's paintings. It was as personal a story as he's ever done.”

12. KUBRICK TEMPORARILY BANNED CRUISE FROM THE SET.

Given his penchant for accuracy, it’s quite possible that Kubrick wanted to stir up some real-life jealousy between his stars in order to help them embody their characters. In a fantasy sequence, Kidman’s character has sex with another man, which motivates the rest of the film’s plot. Kubrick banned Cruise from the set on the days that Kidman shot the scene with a male model. They spent six days filming the one-minute scene. Kubrick also forbid Kidman from telling Cruise any details about it.

13. IT TOOK 95 TAKES FOR CRUISE TO WALK IN THE DOOR.

Six days for a one-minute scene is nothing compared to the time Kubrick had Cruise do 95 takes of one simple action: walking through a door. After watching the playback, he apparently told Cruise, “Hey, Tom, stick with me, I’ll make you a star.”

14. SECURITY ON THE SET WAS TIGHT.

Aside from Kubrick, Kidman, Cruise, and their tiny crew, no one was allowed on the set, which was heavily guarded. In May 1997, one photographer managed to capture a picture of Cruise standing next to a man that the photographer thought was just an “old guy, scruffy with an anorak and a beard.” That man was Kubrick, who hadn’t been photographed in 17 years. After the incident, security on the set was tripled.

15. PAUL THOMAS ANDERSON SPENT SOME TIME ON THE SET.

One person Cruise did manage to sneak onto the set was his future Magnolia director, Paul Thomas Anderson. While there, Anderson asked Kubrick, “Do you always work with so few people?” Kubrick responded, “Why? How many people do you need?” Anderson then recalled feeling “like such a Hollywood a**hole.”

16. KUBRICK HAS A CAMEO IN THE MOVIE.

He’s not credited, but the film’s director can be seen sitting in a booth at the Sonata Café.

17. KUBRICK PASSED AWAY LESS THAN A WEEK AFTER SHOWING THE STUDIO HIS CUT.

Kubrick died less than a week after showing what would be his final cut of the film to Warner Bros. No one can say how much he would have kept editing the film. One thing that was changed after his death: bodies in the orgy scene were digitally altered so that the movie could be released with an R (rather than an NC-17) rating. Although many claim that Kubrick intended to do this, too. According to Kidman, "I think Stanley would have been tinkering with it for the next 20 years. He was still tinkering with movies he made decades ago. He was never finished. It was never perfect enough.”

18. BY THE TIME THE FILM WAS RELEASED, A DOZEN YEARS HAD PASSED SINCE KUBRICK’S LAST EFFORT.

Eyes Wide Shut came out a full 12 years after Kubrick’s previous film, 1987's Full Metal Jacket.

19. EYES WIDE SHUT TOPPED THE BOX OFFICE.

The film earned $30,196,742 during its first week in release, which was enough to take the box office’s number one spot—making it Kubrick’s only film to do so.

20. CRUISE DIDN’T LIKE DR. HARFORD.

One year after the film’s release, Cruise admitted that he “didn’t like playing Dr. Bill. I didn’t like him. It was unpleasant. But I would have absolutely kicked myself if I hadn’t done this.”