I went along to the performance of "Don't Stray from the Path" at the Vault Festival last week, just behind Waterloo Station.
It basically was an interactive story tale, where you followed Little Red Riding Hood on the way to her Granny's house.
It was really well done, and really well executed, but I kind of felt like I was in the middle of a bad dream, so needless to say, an hour was long enough for me!
A lot of work went into it, set design, and loads of actors, wandering around you, trying to get you involved.
Well worth a tenner, if you are into that kind of thing.