How about a scavenger hunt? Working as a team, you solve riddles while exploring the city. Another rather unusual tour is The Ghost Walk. The stories about the Schipfe Poltergeist definitely aren't for the faint-hearted. If, however, you crave a little action, laser tag or paintball are both good options.
Alternatively, pay the Zurich Wildlife Park a visit where you can watch bears, wolves and the like in near pritine conditions or make the short trip to the amazing Bruno Weber sculpture park. On the other hand, if that all sounds like too much work, relax in some hot water on the outdoor rooftop of a thermal bath and enjoy excellent vistas of Zurich.