A creativity / storytelling / extemporaneous speaking exercise.
Take your class on a tour of your school. The catch: they're the tour guides. Make a circuit around the campus, and let individuals stop the tour when they approach a location where they can tell a story, real or imagined, about its significance or history.
If you want to emphasize spontaneity, give about five minutes to prepare, with a notecard for those who need it. If you want a more polished presentation (as a practice, say, for upcoming speeches), give students a day's notice.
The ground rules:
1. Careful in the hallways.
2. Be nice. Don't rag on a teacher you despise. Don't embarrass friends or strangers.
3. Don't monopolize the time. Keep your story under two minutes.
4. Ham it up.
You'll be surprised what you'll learn about your school--and your students.