I would second (or third) the zip line. We also did the ropes/tree top course and it was a fun afternoon. If you can leave the mountain, I would highly recommend the via ferrata at the National Park. It was terrific- beautiful views and a bit less "manufactured" nature than the zip line. It's similar to rock climbing but requires less technical skill.

Edited to add: i also hiked most of the trails on the mountain. Very challenging and bring bug spray. Lots of little flying things that bite.