The theater is situated in the food court, at the metro level. Museums and Monuments DC hosts some of the best museums in the world and they re almost all free. Highlights of the Smithsonian include the National Gallery of Art, the Air and Space Museum, the Natural History Museum where you can view the Hope Diamond and the American History Museum where the First Ladies Inaugural Balls are on display. The Holocaust Museum is also free, but requires advanced tickets for specific times. Make sure you leave several hours to complete the tour.
Admission is free.
The monuments are also open to the public through the evenings. In fact, the best time to visit is after the crowds and humidity have died down. The Korean and Vietnam Memorials are also located on the National Mall. 66 West to Rt. The City Paper is a great resource.