I have ideas for badges that acknowledge activities which are equivalent to famous achievements in their field.
For example, a grey badge could be awarded for a climbing session which achieves the equivalent elevation of a Mount Everest, Ben Nevis, Mount Fuji climb. If the activity is taken in the actual vicinity of said peak, a gold badge could be awarded. Walking badges could be awarded featuring the Inca Trail. Diving badges could be awarded for diving at famous sites such as Ras Mohammed and Elphinstone Reef in the Red Sea.