Plan a scavenger hunt for sounds! Gather a bunch of small tape recorders (PDA's and cell phones might work if they have a recording feature), and send the teenagers out in teams of 3 or 4. Their job is to record sounds you designate like "A Baby Crying", "A Fog Horn", or "A Dog Barking". If you have parents that are willing to volunteer, give each team a driver and let them use the entire city. They must be back before the deadline, and the team with the most sounds wins!