The family that runs the planetarium is incredibly friendly and helpful. They go to great lengths to make you comfortable in the cold (blankets and tea included), and are very enthusiastic. The indoor presentation didn't have too much information, but really I think that's because most of the information about the Inca is unknown. Much of what they share is stuff you will hear elsewhere while traveling through this area. The best part was looking through the telescopes at the star clusters and Saturn (which was cool, but as you would expect, brief.) If you don't have much time in Cusco I would probably skip it.