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This is quite literally off the wall. The "Earth Harp" attaches it's strings, which can be hundreds of feet long, to buildings or whatever, incorporating them into the instrument. They use resined gloves instead of bows. They have other videos on youtube, including some pretty colorful stuff by the sculptural instrument ensemble MASS. Some of those clips offer much better sound recording, but I posted this one because they introduce the thing, explain and demonstrate
http://psalterystrings.ning.com/video/mass-earth-harp-outdoor
MASS Earth Harp Outdoor Performances
Mass Ensemble, Largest Earth Harp on the Planet
Earth Harp Live Clip - MASS Ensemble
Gathering MASS , Earth Harp Description, Oh yeah