Maybe go to Tyson's Corner mall if shopping, or window shopping is your thing, and have lunch and/or dinner or catch a movie. I wouldn't wander too far, as beltway traffic can back up in a heartbeat!

It might help to know your interests, but I'll suggest a military history day trip.

Start out by driving to the National Museum of the Marine Corps in Triangle, VA (about 1 hour from Dulles Airport). This is an excellent (and free) museum that has many interesting exhibits. www.usmcmuseum.com

Then drive to Manassas Battlefield Park (about 45 minutes from the Marine Corps museum). Tour the visitors center before it closes at 5pm and then you can walk and/or drive around the battlefield until dusk. There are also some nice hiking trails. www.nps.gov/mana

The drive from Manassas Battlefield to Dulles Airport should take about 30 minutes.

Thank you guys ! Very much. But I do not shop not interested in war neither.

Udvar Hazy aviation museum is worth a couple of hours.

Go to Great Falls of the Potomac and take a hike, see the canal system that bypassed them, just a couple of miles from DC.

Go west! Take a drive into Loudoun County---if you like wine you'll find 25 wineries in the County. (FYI-Dulles is in Loudoun County.) You can do tastings or just enjoy the scenery---Bluemont Vineyard has great views even if you do not drink. Take in lunch at Magnolia's (an old mill that has been repurposed) in Purcellville, a quaint little town about 30 minutes west of Dulles. Visit historic downtown Leesburg and visit Magnolia's big sister, Tuscarora Mill restaurant where you are sure to get a good meal. Take in some of Leesburg's antique shops or Washington Redskin's Chris Cooley pottery shop in the heart of Leesburg on King Street.

See this site for more details! www.visitloudoun.org

When you return to Dulles, use the Black Diamond security entrance on the baggage claim level. This spot is near baggage claim belt #8 and is a much faster way to clear security when the main checkpoint (upstairs) is busy.

Have fun!

Thank you all, now is difficult for me too choose, I ve been in the Museum one time in the past, I loved it; I also am interested in hiking and visiting little towns. Thank you also for the tip on airport Ranky !
Best wishes to all.