As well as viewing an old building you can enjoy a drink or a meal in a very friendly cafe. There are tables in the courtyard if the weather is fine. There is also a small artisan store where you can get your souvenirs.
We stayed for two days in Puno and went there for breakfast and dinner. Both. Times it was excellent. Beautiful courtyard and nice interiors, good food and great coffee. A little oasis in an otherwise just OK town.