Some would say the journey is more important than the destination, but this rule doesn't apply to 19;29's Threshold, a choose-your-own-adventure psychodrama presenting the implosion of a rich family with more skeletons than hangers in their closets in a beautiful, undisclosed mystery location (I could disclose it, but I don't think I'm supposed to). The twist? To get to the house of horrors you have to take a hour-plus bus ride, regaled all the while with an increasingly insistent audio collage which seems to be mostly about men and women but also features quite a long skit about taxidermy. For some this might be a lot to put up with, but if you can grin and bear the travel time it gets a lot better. And believe me: I was surprised myself. To be honest, I'm quite the curmudgeon and when it comes to it, theatre being poked, prodded and breathed on isn't high on my to-do list. Not to mention running.All of which means I was more than usually impressed with Threshold, a piece so fully immersive (for one character, even submersive) and so fully site-specific that it has the power to convert any sceptic. After an hour of jogging, climbing over tree roots and getting chained up by a housekeeper named Badger, it was impossible to imagine this show taking place anywhere other than in this house and its gardens the company used the space so effectively that the lines between fantasy and reality began to blur. Have you ever said 'thank you' to a cash machine? The conversations this piece encourages between spectator and character may provide a surprisingly similar experience. Fourth wall? What walls? We're literally in the woods. It feels ridiculous to talk in terms of scenes with a script like this, not least because the way the audience is divided between our four guides Samuel, Lara, Ludo and James meant each audience member would always have multiple pieces of the puzzle missing. To point out that the story is based on the Bluebeard myth may help, but certainly won't alter the grim inevitability of its development. I can only review the sections I saw, but without giving too much away, I was convinced by Lara's childish energy and terror, captivated by the sense of ceremony at the central wedding rituals, and literally didn't know where to look when led away by Badger at the end of a dogleash, an experience most punters probably won't get to share.The performance doesn't stop when you leave the space either, but the bus journey back is generally a less irritating affair. The general drift of this kind of theatre is often towards breaking the barrier between actors and audience, but this show does something more interesting and more novel; it breaks down the walls of silence between audience and audience, releasing viewers (and reviewers) from their monadic private world as spontaneous conversations break out on the coach home: What did you see? Whom did you follow? What happened to you on the ground behind the maze? All of these questions or none may be answered in the next performance of Threshold, but if you've got time to spare and can deal with the audio collage, the interaction and the occasional bout of light running, it's a fascinating and unusual afternoon out.