Gym Challenge

Hero level 30 unlocks the gym. In total, there are 8 gyms to defeat. Collect Badge Stones by defeating the members inside the gym, then enhance your badge until it is max level. You can only defeat the gym once per day. Skip a day's worth of defeating with diamonds, but as you advance badges, it becomes more expensive to do so.

Once you've completed all 8 badges, you're able to revisit the last gym and collect Badge Stones, however it has no effect.