If you’re visiting the Smithsonian museums in Washington, DC, I encourage a brief detour to the oft-overlooked College Park Air Museum just NE of the city. Based at the oldest continuously operated airport in the US, it has a delightful little museum staffed by some very knowledgeable and friendly volunteers and a small collection of interesting aircraft and artifacts. I volunteered there while in graduate school (studying the history of aviation, naturally) and always looked forward to spending my Saturdays chatting with visitors, perusing their library, and visiting their restoration shop.