It's always difficult coming to a large metropolitan area that has many military installations. Hopefully, the map below will help give you some geographic perspective.
Installations located in Virginia are: Fort Myer (Arlington), Henderson Hall (Arlington),
Pentagon (Arlington), Fort Belvoir (Alexandria / Mount Vernon), and Quantico
(Quantico in Stafford County)
Installations located in Maryland are: Walter Reed National Naval Medical Center (Bethesda), Joint Base Andrews/Andrews AFB (Prince Georges County)
Installations located in Washington, DC are: Fort McNair, Washington Navy Yard, Bolling AFB