Alternative Reality Games Intrigue Me:
The Witness is an alternative reality game that uses specially designed iPhone software to display a film when viewers/ players are standing in the location where events of the narrative play out. Players/ viewers assumed the role of detectives and traveled to locations around Berlin to unlock additional videos in this choose your own adventure style game.
The video describes the experience far better than I do:
I think it would be cool if more experiences like this were available. Perhaps I'll create something similar.
Also, I think it would be cool if someone did something similar inside a haunted house or at several "haunted" locations around town in the month leading up to Halloween.