Watching a film at the cinema is largely a passive activity, right? You sit back in your seat at the local fleapit or multiplex, munching on snacks, and let the film wash over you. The film ends, you get up and leave.

The folks at Secret Cinema think differently though - they think that the experience of watching a film should be just that - an experience. Since 2007 they've been creating interactive experiences for film-goers, blending the worlds of cinema, theatre and cabaret into single events.

They start by finding a unique location, and then work outwards from there to see what classic film most suits that building or space. They then build a dramatic world around their chosen film, creating site-specific sets and narratives inspired by it, all fleshed out with a host of talented actors. Instead of just watching a film, the audience interacts with the space, the sets and the cast, before, during, and after watching the movie; a sort of immersive cinema.

With each event, you don't find out what the film is until you get to the location. Hints are dropped in the lead up to the events, through a mix of websites, social media, and warm-up happenings, but to be honest, everyone is generally still guessing until they get there (hence the name).

The latest Secret Cinema show (their twentieth) kicked off a couple of weeks ago in London, and we went along last week to check it out.

Now, of course, because of their policy of secrecy, it's a tad tricky to review one of their events until after it's finished its run. If you do a full review, you totally give the game away, and risk spoiling it for anyone who's not yet been.

So, we're going to talk about the build-up to the event (let's call it SC20), and talk in general terms about how it felt to be there. We're not going to tell you what the film is, nor mention anything too specific, but if you want to steer clear of knowing anything at all about it, you might want to skip the rest of this post.

We were initially booked in to go along on during the opening week, but due to a last minute licensing issue, the first few shows were cancelled. Given the massive complexity of putting on a show of this kind, that must have been a nightmare for the organisers, but judging from the online chit-chat it was for ticket holders too, many of whom had booked time off work and travelled fair distances to attend. To their credit, the SC team put on a replacement screening of Footloose over the weekend by way of apology, and offered replacement tickets too - but it shows the risks you run when you're putting on such unique events.

For the online and social media side of SC20, we were asked to log-in to the G.O.O.D. Intranet system, where we had to fill out a work appraisal, as new employees of the G.O.O.D. organisation. This created a unique Social ID number which would provide access to the event.

All new employees were also invited to attend a global gathering warm-up event in London's Docklands, and directed to a video showing dance instructions for a collective dance based on the promo for Atoms for Peace's track Ingenue, featuring Thom Yorke's singular dance moves.

We didn't make it along to the warm-up, but a fair few folk did, and it looked like a fun old time.

Of course, this left us wondering whether Secret Cinema were doing something different with SC20 - was it going to be an Atoms for Peace gig instead of a movie? Or perhaps something to do with music videos? Based on our experience, these were red herrings - though the music and the dance did still form a hugely enjoyable part of the evening. But there's definitely an art to managing the expectations of an audience for a secret event - if you hint at something that isn't going to happen, you risk leaving people feeling disappointed.

Having logged in to the G.O.O.D. Intranet system (and following the organisation on Facebook and Twitter) we were issued with a Notice of Transfer, which detailed all the preparations we had to make for the event. The specifics differed for each person, but everyone was asked to dress up, and to prepare business cards and an ID badge. We were also asked to connect to other employees via the intranet, each connection increasing your 'rank' in the organisation.

Again, there's a trick to getting that sort of thing right - on the one hand, there's a definite sense that the more effort you put in beforehand, the more fun you have when you get there. But on the other hand, there's a vague feeling that some of it is just fluff, and that your efforts aren't fully recognised on the night, and that feels like a shame and a missed opportunity.

So, the event itself. We don't want to tell you too much. But it was certainly great fun.

It was less of a movie screening, more of a site-specific interactive theatre event. The movie is screened in part, but we decided not to sit down and watch it - there was too much other interesting stuff to be doing. One of us hadn't seen the movie before, and the other had, and it definitely felt like familiarity with the movie added a huge amount to the experience, but that it wasn't absolutely essential.

The location is on the outskirts of town, but not beyond the bounds of an Oyster card. The set building within the space is really extensive, including bars, a restaurant, interactive technology, dance performances, installations and more. Some of it is really slick, but other parts are enjoyably lo-fi.

Upon arrival, audience members are sent to various different entrances. So if you go as a group, you're likely to be separated from the start - though you can meet up again once you're inside.

Following on from the online stuff, the plot of the evening is that you're a new employee on your first day at a new company. There's a lot of interaction with the actors, all of whom manage to pull you in to their narrative without making you feel awkward or patronised. They give you small nudges as to where you might head next within the space, gently giving shape to your overall experience.

Because you're free to roam, everyone has a slightly different experience of the evening. The more you explore, the more fun you have. There were a few shared moments when everyone in the building was doing the same thing, and there's a very clear climax to the event too.

All in all, it's a great night out. Just don't go along expecting to sit down quietly and watch a movie.