The Hirshorn is a a modern art museum that is a part of the Smithsonian Institution, located in Washington, D.C.. Perhaps the most striking thing about the museum is the building itself. The building is shaped like a hollow cylinder. While walking through an exhibit, you will slowly spiral up or down the inside of the building. The building does not have supports everywhere around its base, but just at a few points. So picture this: you're standing in the middle of the Hirshorn Museum courtyard. You look up, and can see the building all around you, and the sky in the center. You can look all around you, on ground level, and see only a few pillars sticking up from the ground. And various pieces of art scattered about.
Oh yeah, it's an art museum. Well, it's got lots of it, most of it modern. According to their website (http://hirshorn.si.edu/) they have "one of the most comprehensive collections of modern sculpture in the United States or abroad". They also have paintings from the late 1800s to the present.
A good bit of their sculpture is actually in a sculpture garden across the street from the museum itself. The garden is on the mall, and is sunken into the ground, making it isolated and more museum-like than a normal open space.
Yes, and in case there was any doubt, it's named after the guy who gave the money and art, Joseph Hirshhorn (1899-1981).