Hotel Katari
For the view
Regardless of where you are staying, you should go up to the rooftop bar on Hotel Katari to watch the sunset over the volcanos.
There is a fabulous view of the Plaza de Armas and cathedral framed by the Misti and Chachani volcanos.
I took the photo above at the end of November, which is supposedly the rainy season. However, I had sunny days the whole week I was in Arequipa.
Tables are limited, so plan to get there about an hour before sunset. There is a s/50 minimum per table, so be ready to order some food or cocktails while you watch the volcanos turn pink.