The Telephone Call, Janet Cardiff, San Francisco Museum Of Modern Art, June 2001.

You handed in some ID and a credit card, and you were issued with a video camera and headphones. You put on the headphones, sat on a bench and stared at the screen on the camera. The screen showed a view of the interior of the museum, from where you sat. Instructions in the headphones told you where to go, and where to point the camera. It was a wierd experience, looking in the camera and seeing the same space, but with different people. It was also strange to be instructed to walk though a door marked "Private, Staff only", and to be separated from the rest of the museum, to stand on you own, on bare stairs and suddenly be approached by foot steps from behind. Except the footsteps were only on the soundtrack, and not in the real world. Very interesting.

More info at: http://www.wired.com/news/culture/0,1284,42152,00.html