National Air and Space Museum

The Smithsonian's National Air and Space Museum is a must see. Even if you don't have kids! The wonder of this place brings flight and science to life. They have two locations that I know of:

National Air and Space Museum
601 Independence Avenue Southwest
Washington, DC 20472
(202) 357-1387

and

Smithsonian National Air & Space Museum
Steven F. Udvar-Hazy Center
Air & Space Museum Parkway
Fairfax, VA 20151
(703) 572-4118

And, if you're a Star Trek fan like me, this alone, is worth the trip! Pictured below is the model of the USS Enterprise used in the production of the original series!