26.2 miles? Do you have to train?

I posed this challenge on Facebook after watching an episode of "How I Met Your Mother?" where Barney runs the NYC Marathon in a decent time without training. I know this is a sitcom, but it presented an interesting challenge for a non-distance runner.

I remember growing up watching the Philadelphia marathon and thinking that running to Center City was pretty far. Now that I'm an adult, it doesn't seem that far.

OK. I'm going to try it for the sake of just seeing how my body is going to react. My Facebook friends have suggested upcoming marathons.