I'm running the Lincoln Tunnel 5K race in April in New York City. If you aren't familiar with the Lincoln Tunnel, it's a long tunnel under the Hudson river that connects New Jersey and Manhattan. Every other time, it's packed to the gills with cars, but they're closing it for an hour or so for the race. I found this race through Runner's World.
This is one of those races that you do because you would otherwise never have a chance to run it. It's not everybody that can say you've run through the Lincoln Tunnel. It's not a long race and won't require any sort of training, but for what it lacks in distance, it makes up for in "kitsch factor".