i meant this more in the sense of "what's a piece of code you've seen(or written) that made you excited and made you think 'wow that's really clever!'" It shouldn't necessarily be something earth shattering, could be very simple, just something you genuinely liked. I personally believe enthusiasm (including intellectual curiosity) is the most important quality somebody can have in the workplace.

If your problem with the question is trying to think of a response that the interviewer would want to hear, then you aren't approaching the question correctly and/or neither is the interviewer.