I *might* be able to do 10 hrs at PDX (rocking chairs, live music, decent restaurants) but 10 hrs at IAD? Never. Lousy seating, lousy food, just horrible. Hate IAD.

If your flight lands at 7, you won't be out of the airport until at least 8:30, and then RUSH HOUR into the city. Figure an hour without traffic. So that's 9:30 at the earliest.

If you have an outbound flight at five, that means leaving the city by 3; maybe a little earlier if you do Metro rather than taxi. For an international flight leaving at that time of day, I would err on the side of being early.

So you would have about six hours. I'm thinking that if you wanted to do something specific in DC, it would be OK but if you just want to wander around, kind of pointless. I think the Udvar Hazy Air & Space out near Dulles would be a good idea.

I just checked the IAD website. No luggage storage. That's an issue.