Clearly, you don’t want to go on and on with any one answer. So figure out your key points ahead of time, and do your best to keep your response to a few minutes tops.
Also, you don’t want to sound like a one-man (or one-woman) show. Talk about yourself within the context of the organization in a way that highlights your abilities and confidence in what you’re good at, but it shouldn’t come off as bragging. Or that the co-workers were lost without your brilliance. As great as you may be, you still need others to want to work with you.
And if your greatest accomplishment to date happened outside the work arena, that’s a perfectly fine choice. Just make sure that in your answer you find ways to connect your skills / talents to where you want to go next!