Musical Plaza w/ tangibles
image from here
How about a plaza, with each bench, bush, etc a tangible object on a huge reacTable? Add in some humans, dogs, pigeons, and track them as tangibles, too, based on blob shape. An aerial view of a park becomes a sound canvas. Now pipe the sounds in over xmitters in the park, sending to optional headsets. Let people make their own soundtrack - quiet and reflective for reading a paper on a bench as runners zizz by. Picking up more as the commute thickens. Quiet at night, expcept in cases of sudden movement.