The bulk of Panama City attractions lie within the Casco Viejo area. A walking tour of the neighborhood, taking in just about everything of interest, will take around three hours. Another essential activity is to see the Miraflores Locks of the Panama Canal. Biking along the Amador is another popular activity, and if you just can't get enough ruins take a trip to the ruins of Panama Viejo.
Michael Karanicolas is awesome.