A museum in Washington, D.C., and one of the few museums in that city that is not a part of the Smithsonian Institution (although it is still located on the mall). It's got two wings: the East wing and the West wing. Actually, while the museum refers to them as "Wings", for all intents and purposes they are separate buildings that are connected by an underground tunnel.
The West building is the "old" wing, in that it has the European-style art from the middle ages until impressionism. It is also "old" in the sense that the building itself is modeled to be like the louvre museum, in that there's a central fountain and large marble staircases. Of course, they're just kidding themselves: the Louvre is a lot bigger and has more paintings. But it's the thought that counts. They do have some nice pieces by Monet and his impressionistic crew, so that's worth something.
The East building is "new", both in artwork and design. They have various exhibits from the 20th century. Their most memorable permanent piece of artwork is an Alexander Calder mobile: one of those huge, hanging things made of brightly colored metal. The building itself is quite spectacular; it was designed by I.M. Pei. It has a triangular motif: the building itself looks like a triangle if viewed from the air. In addition, in between the East and West buildings are several glass pyramids, which are both beautiful and functional: they serve as skylights for the underground connecting walkway. (Incidentally, I.M. Pei also designed the glass pyramid in front of the Louvre. Coincidence? I think not.).
More info at http://www.nga.gov