I was attending a production of Faust. It wasn't really a play as such - more of an interactive experience. The rules of the game are as follows:

• It takes place over five floors in an abandoned warehouse
• The audience all wear white masks, to distinguish them from the performers
• As a member of the audience, you are free to wander where you will, watch what you want to watch, follow people and explore the scenery

We entered the building, walked down a set of steps into the dark and then through a door into, unexpectedly, an old western-style bar complete with band, tables with candles, wooden plank walls and some young ladies serving strong liquor (or some nice wine, if you prefer). We were given the masks (which owe more to Scream and Donnie Darko than Phantom of the Opera) and walked out into a very large lift, accompanied by a young chap with a southern drawl called Jeb who gave us an idea of the layout. Three people were allowed out on the third floor, four on the second, and so forth. We escaped onto the ground floor to find ourselves next to a western-style diner, just along from a store, a bar and a small fully-functional cinema.

While wandering around the diner, a man touched me on the shoulder and beckoned me over to a door marked "Staff Only". I followed him through, into a darkened cupboard where he removed a plank from the far wall and led me through to a hidden room. I won't go into details about what exactly happened, but it is a very intense experience having  a one-person audience with a malevolent angel whispering blood-curdling sentences into your ear.

Exploring the rest of the building was alternately fascinating (exploring the sets, which were full of detail and atmosphere), creepy (especially walking through a darkened maze of filing shelves) and frustrating (when trying to figure out what the hell was going on). There were bursts of excitement as someone not wearing a mask strode past us and off into the distance, melting away into the shadows before they could be followed.  Having an older Faust walk into his laboratory as you are sitting at his desk looking through his microscope was unexpected; the actors generally ignore the audience but sometimes interact with them, quietly pass on clues as to what is happening, dance around them, push them out of the way or simply mutter monologues.

There is an element of a jigsaw about the whole thing, although you can never pick up all the pieces of the play as many happen concurrently. This can either annoy or engage; the aim is to try and figure things out but allowing yourself to experience it without too much in the way of analysis is probably the best approach.

The only criticism that I had was that there was rather too much dance for my liking; I'm not a great fan of expressing plot via the art of dance. These scenes were at least well done and could be accepted within the atmosphere created; if they were on a stage or in a well lit room I may have sniggered instead of being engaged.

Overall: if you would like a completely different experience from almost anything else you have ever done, I would thoroughly recommend it.

Other reviews: Guardian, Telegraph, Observer, Spank the Monkey