There isn’t much to do in Puno, Peru other than await your trip to Lake Titicaca and run around getting the American dollars and the photocopies you need after deciding to head to Bolivia (because Americans have to pay $135 and provide copies of their passport at the border. No one else, mind you. Just Americans.)
Sillustani is a pre-Inkan burial ground just outside of Puno and everyone offers a quick day trip there for around 30 soles (about $11). With an afternoon free I hopped on the tour with some others from my hostel.
We walked up to the top of the hill to look at the chullpas, graves, wandered the grounds, and stopped at a typical house on the way back to eat some salty local cheese and pet some alpacas.