Your favorite single act of Wagner

What is your favorite single act of a Wagner opera?

Here's the context, for those who want it. My five-year-old just read about Wagner in a book and now wants to listen to some. But he's not going to have the attention span for an entire opera, so I want to pick one act that we can listen to while reading the story (or doing that before or after) and then watch a production. We've done this with Mozart and Handel and he's loved it. The problem for me is that I love Wagner and can't decide what to use, and I'm hoping for a little help. Plus, I think it's kind of a fun desert-island-style question. Thanks for your help.