Thanks, guys.
Forgot to post a follow-up. I did ride DC at night for a bit; was with the wife and kid, so it was just the mall. Next time I'm alone, I'll brave the streets and check out the area a bit more.
Fountainhead was a decent ride, did all 3 loops and hit green for a 2nd run and legs were worked out. Nothing terribly difficult, but a pretty nice ride with the water nearby. I agree with the downhill runs being extremely short; I think there were maybe 2 good dh runs before having to pedal again.
I think next time I'm in the area I'll hit the Frederick Watershed.
Thanks again