Check out the Chocolate Museum and the drinking chocolate there. As has been mentioned, there are daytours to nearby Inca sites. When I went there there always seemed to be something happening on the Plaza de Armas...one day it was a costumed parade, the next a protest over a mine that some company is trying to build.

'Tis also helpful to be on the lookout for authentic sorts of experiences...in my case it was being able to watch a Peru vs. Colombia football game at a sports bar. Locals were really into that one.