As any fan of the Harry Potter books and films can tell you, the wonders of the wizarding world are a closely guarded secret, with all manner of magic deployed to keep the muggles unaware of the wand-wielders among them.

And a similar level of secrecy surrounds Harry’s first on-stage outing, Harry Potter and the Cursed Child, set 19 years after the last book ends. After enchanting audiences on Broadway and breaking awards records in London, it’s now showing in Melbourne, the third city to host the smash-hit play. Since opening in February to rave reviews, demand for tickets has been huge – so much so that 50,000 more were recently released.

With almost six hours of spoilers to protect over its two parts, theatregoers (and this journalist) have been asked to keep the show’s twists and turns under wraps, or #KeepTheSecrets. It’s a big ask considering the number of people keeping those secrets is already in the tens of thousands just a few months into the Cursed Child’s indefinite run at the Princess Theatre.

For the show’s creators, though, ambition of this scale is familiar territory. From the impressive technical elements to the collaborations between costume, set and special effects designers, to the huge variety of different stagecrafts in use at any one moment, this show breaks new ground. And not just on stage.

More than $6.5 million has gone into refurbishing the Princess Theatre for Cursed Child. Its foyers and front of house have undergone a top to bottom Hogwartsian refit, so you’re immersed in Harry’s world as soon as you cross the threshold. Custom lighting fixtures represent Hogwarts’s four houses, and carpeting with the Hogwarts crest has been laid throughout. A decadent private lounge (which can be hired out for pre-show cocktails and canapes) is by interior designer Geraldine Maher, who designed the new bars at the Forum Theatre.

In a way few other productions have, Cursed Child ups the ante of the audience experience. The man behind this magic, technical director Cameron Flint, oversaw the show’s Down Under debut, including the refit of the Princess.

“This was seriously magnified. I can’t go into too much detail, but I can safely say there are few corners of the building that went untouched,” Flint says. “On a normal show there’d usually be a small degree of venue modification required, but this was on an unprecedented scale.”

A tonne of work goes into ensuring the show’s special effects go off without a hitch. Some scenes could be potentially dangerous for both cast and crew – flames, haze and great heights feature heavily – so contingency options are in place to keep the show on track and the actors safe.

“There was a wonderful moment when, after 10 long weeks of bump-in [installing the sets] and dry tech [running the show without the cast], the actors finished in the rehearsal studio and joined us in the theatre,” says Flint. “Two worlds collided. They were gobsmacked.”

Pulling off a show of this scale and complexity takes some serious people power. More than 100 professionals come together for every performance, including 50 permanent show crew and a mammoth cast of 42 actors.

Playing the role of Hermione Granger is award-winning actress Paula Arundell, who’s starred in productions for Sydney Theatre Company, Melbourne Theatre Company and Bell Shakespeare. But taking part in Cursed Child is unlike anything Arundell’s experienced before. “Going to rehearsals was like turning up to a surprise party every day,” she says. “Even though you’re being talked through how certain moments work, how they achieve a particular effect, it still feels like there is some legitimate magic going on in front of you.”

Arundell says developing the role of Hermione was a unique challenge, taking into account the expectations audiences bring with them to the theatre. She had almost no knowledge of the Harry Potter novels before joining the cast, but this ultimately turned out to be an advantage.

“That felt quite apt for Hermione, you know? She’s not interested in herself or what’s popular,” Arundell says. “She’s incredibly driven and can be totally obsessed with the things she loves.”

At the other end of the spectrum, Nowhere Boys, Jindabyne and Utopia actor Sean Rees-Wemyss, who plays Albus Potter, Harry’s youngest son, has long been a super-fan. He says beginning rehearsals was like enrolling at Hogwarts. “The coolest thing was getting schedules, because they looked exactly like a school timetable: ‘10.30 – flying class. 12.45 – wand work’. We had all this extra training to be show-fit, which is not something I’m used to. It was really intense, but also, so, so cool.”

Rees-Wemyss is on stage for a lot of the almost six-hour show. In preparation for the role, he reached out to one of the few actors he knew who could relate: Sam Clemmett, who played Albus during the show’s premiere season in the West End. “The most important tip from him has been about taking good care of your body and your mental wellbeing. I feel so lucky to be part of this production, but if I didn’t take care of myself, doing eight shows a week would quickly get pretty tough,” he says.

“It’s also about doing right by Albus. He’s such a meaty, rich, fascinating character. I get to be in his skin every night and I’m always learning something new about him. And if I don’t feel that, if I’m not focused for whatever reason, that’s when I know I’m letting him down … He’s a pretty fragile guy, he needs looking after,” Rees-Wemyss says. “I know that sounds incredibly strange, but I guess that’s just a testament to how fully realised the world of this play is.”

Beyond the stage and the stunning venue, many Potterheads come to the show fully prepared, too, dressed in full Hogwarts uniform complete with wands, broomsticks and the occasional cauldron. Having booked tickets sometimes months in advance, many are nervous, waiting with anticipation to see how the books they grew up reading translate to the stage, wearing their Potter-loving hearts on their robed sleeves. This perhaps unintentional final touch leaves you just that little bit more immersed in the Harry Potter universe, in case you weren’t already.