Have you ever become so obsessed with a television show that you wish you could be transported to its fictional world, walk along its streets and hang out with the characters? If, like so much of the TV-watching planet, the show is Stranger Things, then Secret Cinema has made this fantasy come true.

Launched in 2007 by Fabien Riggall, Secret Cinema has created extravagant immersive experiences for a bundle of popular films, including Blade Runner, The Third Man and Casino Royale. Its outlandish productions blur the line between film and theatre: elaborate sets and mingling actors draw you into the world of a movie before you’re led through it to a screening. “When you watch a play, actors on stage perform at you, but at Secret Cinema they perform with you,” says Riggall. “You’re given the chance to perform back to them and become part of the story. The film comes alive around you.”

The Stranger Things event is Secret Cinema’s first venture away from film into television, and it is an inspired choice. Somehow both zeitgeisty and drenched in nostalgia, Netflix’s phenomenally successful show has an immense universe full of weird and wonderful characters, monsters and stories that can be brought to life; sinister scientists, malevolent Russians, the paranoia of Reagan-era politics and the vivid retro appeal of the 1980s all play a part.

Then there’s the Upside Down, another dimension that runs parallel to the fictional town of Hawkins, Indiana. “Hawkins is a really great evocative place,” says Secret Cinema’s creative director, Matthew Bennett. “There are more principal characters in this than you would ever get in a film. This is a world that wants to get built. We’ve not had to force it into existence, it explodes into existence.”

Sinister scientists, malevolent Russians, the paranoia of Reagan-era politics and the vivid retro appeal of the 1980s all play a part.

Unfortunately, Secret Cinema’s Stranger Things event is almost as mysterious as the show, making it tricky to explain specifically what’s special about it. Pretty much everything is a closely guarded secret: the characters you’ll meet, what you’ll experience, and even the precise location, in London, are all revealed at the last minute.

Noah Schnapp and Caleb McLaughlin at the Stranger Things Season Three premiere in June.

The narrative begins the moment you buy your ticket online. It’s 1985, and you’re invited to a Hawkins High School reunion for Independence Day celebrations. You’re given a character profile instructing you on how to dress and what you need to bring. Some of these only make sense later on — learning the lyrics to The NeverEnding Story pays off joyfully.

Once at the venue, you are given a set of challenges specific to your character. Just like Mike, Dustin and the gang, you have to do sleuthing and find clues. It’s a neat ploy that encourages the audience to engage with the world, talk to the actors and uncover secret rooms. These rooms are well worth discovering — memorable moments from the show are delightfully recreated and will make superfans squeal.

The sheer size of the space and complexity of the sets within is impressive. More than 40 actors perform each night, and, during its four-month run, 100,000 people will see it. Tickets come at two levels: standard and VIP. Standard ranges from £52 to £83, inclusive of a booking fee, depending on which night you go; VIP ranges from £104 to £146, offering extras including fast-track entry, two drinks and a meal. There are also discounted tickets for 15- to 17-year-olds at Saturday matinees.

More than 40 actors perform each night, and, during its four-month run, 100,000 people will see it.

It features all the main characters — not played by actors from the show obviously — and all are superbly cast to resemble their on-screen counterparts. The majority of the time they perform large set pieces in the central space, but if you are lucky you can catch them wandering around and strike up a conversation. It’s a little surreal chatting to a fictional character; it can feel vaguely ridiculous, but it’s part of letting yourself get swept up in the story.

The show is set at the end of series three but has its own original storyline. Its script had to be blessed by the creators of Stranger Things — the Duffer brothers — and written in close collaboration with the television show’s chief scriptwriter, Paul Dichter, to make sure it didn’t stray too far from the canon. “The Duffer brothers were really good at allowing us to develop extra secret conspiracies that happen in Hawkins just for our show. So it’s official and new and only exists in our shows,” says Bennett. “And it’s been amazing for Netflix to give us the keys to their No 1 show and let us joy-ride around in it so flamboyantly.”

You will definitely get more out of the evening if you’re familiar with the series; following supplemental narratives and spotting roaming characters adds to the fun. Everything leads up to an explosive finale, breaking with Secret Cinema’s usual format of ending with a screening (it would be exhausting to sit through an entire series). The solution is entirely new, incredibly intense and well worth the secrecy-shrouded wait. “We are aggressively rebooting the tell-no-one principle on this show because the climax is the best secret we’ve had in ages,” says Bennett. “You will never see this on Netflix!”

Secret Cinema Presents Stranger Things runs until February 23 (secretcinema.org)