Originally Posted by
buckeyefanflyer
If it is Washington National there is alot to do since the airport is close to the city sll the muesems. You can catch a train at the airport. If it is Dulles,
they used to have a branch of the air and space museum near the airport, not sure if it still there.
The Udvar-Hazy center is still there at IAD and is well worth a visit. They have a free shuttle bus from the ground transportation area. That's probably the best option for a non-airport activity given the time frame.
Assuming an international arrival and mass transit for transfers to/from downtown ORD would leave about 2 hours to do something downtown; IAD might be less based on the terrible transit options there. But Udvar-Hazy is close and easy to get to and a great way to pass 2-3 hours. There are some pretty impressive planes on display.
http://gallery.millerworks.net/keyword/udvarhazy