1. Not accessible. Not until if there any future dlc which allow you to do so
2. Cant be disable. There is no way to disable anti dragon force field at harbor and high hall for now.
3. As I know there no key for it. Never able to open it during my first run through, nor the current second run through. Mostly just for display. Even can be unlock, might just give you a few extra goblins to kill.
