The first 'Harry Potter' book came out 20 years ago this week -- here are 28 incredible things you never knew about how the 'Harry Potter' movies were made

Harry Potter set Diagon AlleyHenry Blodget / Business InsiderThe real Diagon Alley. It was inspired by Charles Dickens’ books and J.K. Rowling.

The “Harry Potter” franchise turned 20 years old in June. Author JK Rowling was 32 when the first book was published. A series of hit books and movies followed.

Warner Brothers then spent 10 years in Leavesden, UK, filming eight “Harry Potter” films.

The studios are massive and reveal how the movies were made using the most incredible special effects in the film industry.

Over the course of filming, five warehouses full of props were used. There was an Animal Department, a Creatures Department, a Visual and Special Effects Department, and more, which made each detail of JK Rowling’s magical wizarding world come to life.

We visited the studios in England and learned the secrets. Here’s how the producers did it.

The floating candles in the great hall were originally hundreds of real candles suspended by wires, which were digitally removed. But while the first movie was being filmed, there was a problem. The heat from the flames burned through the wires and caused candles to drop onto the tables. Afterward, all the floating candles were created digitally.

During the epic feast in 'Harry Potter and the Goblet of Fire,' tons of desserts covered the tables in the Great Hall. While most of it was made from painted resin, some of it was edible and the cast got to indulge.

In Harry's Gryffindor dorm room, props changed from movie to movie. Producers lined bedside tables and walls with things the characters would be interested in, like sports posters and pennants. But the beds were never upgraded. By the time the final movies were filmed, Daniel Radcliff and the other boys had to curl up in balls to keep from hanging over the edge of the bed during shoots.

Dumbledore's office was intricately designed by producers who bound hundreds of British phone books in leather to fill the bookshelf, and placed 48 portraits on the walls of 'Hogwarts' headmasters.' The memory cabinet, where Dumbledore showed Harry his memories, was decorated with more than 800 tiny, hand-labelled vials.

The potions classroom actually grew in size during the filming of the 'Harry Potter' movies. Producers had to expand the set to make room for all the extras. The hundreds of glass bottles that lined the walls of the classroom were filled by producers with any strange thing they could find, from tufts of hair to unwanted guts or bones from local butchers.

To make Hagrid look giant, producers found a 6'10 double for the actor. They also made two different versions of the sets for his hut. A larger set made other characters like Harry and Hermione seem 'normal' size and a smaller set was used to make Hagrid look large.

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The creations team made this mask for Hagrid's character.

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There was an entire animal productions team used to tame and coach a variety of creatures that appeared in the eight movies. Hedwig, Harry's owl, was played by four different owls who were each taught very specific actions. More than a dozen rats played Scabbers, Ron's pet rat in one of the movies. Four different cats played Hermione's pet, Crookshanks. Nine Neapolitan Mastiffs played Hagrid's one dog, Fang.

To make Ron Weasley's parents' house look disheveled, no walls in the set were at a right angle. Support beams were yanked out of place after the set was built.

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Quiddich was the work of the special effects and visual effects teams. Brooms were mounted in front of a green screen, which the visual effects team could replace post-production with a digital backdrop. Several versions of the golden snitch were designed. The final version was plated in gold.

Five large warehouses were needed to store all of the props used during the 'Harry Potter' films. They included 5,000 pieces of furniture, 12,000 handmade books, 25,000 printed pages of The Quibbler, and 40,000 Weasley's Wizard Wheezes products. Here are the horcruxes.

The goblet of fire is over five feet tall and it was hand-carved from an English Elm tree. More than 3,000 wands were used during filming.

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18 cars were used to film Harry and Ron's getaway sequence in 'The Chamber of Secrets.' Three old double-decker buses were used to build the 22-foot high Knight Bus.

The moving staircases in Hogwarts were a combination of one real staircase and a tiny model of multiple staircases made to look real post-production. The actors stood on this single moving one to film scenes, and the rest were sweeping views of the model.

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The moving portraits in Hogwarts were a mix of real paintings and green screens replaced by moving images, post production. All of the portraits were of producers who worked on the films so they could be immortalised in the movies.

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The Ministry of Magic set was so big, it took hundreds of extras to fill it, including some producers. Walls were lined with green and red tiles made of wood, and the fireplaces where wizards could warp to stand more than nine meters tall.

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In one of the movies, Harry goes to the Ministry of Magic to find a horcrux. There, he finds hundreds of prophecy orbs. 15,000 physical orbs were made and lit by set designers. In the end, all of them were scrapped because the whole scene was digitalized. The studio tour still has some of the originals on display.

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A large 'Magic is Might' statue that crushed 58 muggles was made of foam and hand painted.

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Delores Umbridge, the evil professor who wore pink, had a very pink office in the Ministry of Magic. Dozens of plates with cats painted on them hung on the walls. Only the cats weren't actually painted. Producers snapped photos of cats then digitally implanted them onto the plates during post-production.

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As Umbridge gained more power (and became more evil), her wardrobe got progressively more pink.

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Not everyone in the films was supposed to look like a muggle or wizard. There were tons of creatures, which required an entire creatures shop in set. They spent hours making and putting on masks for the Gringotts goblins.

They also created models of things like Dobby and Mandrake plants that could be scanned into computers by the visual effects department which would then create computer-generated versions.

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All of the creatures began as sketches drawn by the design department. Here's a mockup of Dobby.

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In addition to creating models and masks, the creature shop could actually make the monster models move with motors. The giant spider in one of the movies took motors and about 100 people to move.

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Voldemort's face was half-human, half-digital. Makeup artists covered actor Ralph Fiennes with temporary tattoos for veins and gave him contact lenses, fake eyebrows, nails and teeth. The digital team switched out his nose for snake-like slits.

Diagon Alley, where Harry gets his wand and butter beer, changed throughout years of filming. It was built with Charles Dickens' books in mind, as well as descriptions from the 'Harry Potter' series.

The Weasley's Wizard Wheezes store took three months to build and was filled with 120 designed products. Ollivanders wand shop had more than 17,000 individually labelled wand boxes in it.

To film sweeping views of the fictional Hogwarts castle, the art department built a 1:24 scale model based on a sketch by one of the production designers, Stuart Craig. The castle takes up a massive room and details every courtyard, field and tower filmed in the movies. The towers could be lit inside. Real gravel and plants were used for the landscape. It took 86 artists months to construct.

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