Including not just the National Air & Space Museum, which I visited a lot in the Eighties and Nineties, but also the Air & Space's Udvar-Hazy Center. It's huge and sprawling and it finally opened in 2003, after the Smithsonian had declared back in the 1980s that an annex at Dulles Airport made the most sense as an annex location. More space for bigger planes and craft, plus it'd be easier to get those big craft there if it was at an airport; you can't land a 747 on the National Mall. (Rockets shouldn't land anywhere but their landing platforms, but that's another story, one that Space X and others are writing. But I digress.) For decades Air & Space was storing big items at Dulles, like the space shuttle Enterprise and the SR-71 now on display there, and I waited for an annex to be built.
Selfishly, I kind of wish it had been built while I lived there, only a few miles away, but it eventually got funded (in 1999, by the billionaire the center is named after) and built. It opened in 2003; I've visited it once so far, in March 2004. But it was in my imagination long before then.
Like this: in the late Eighties, around the time a TV series debuted that was a followup to the 1953 film version of War of the Worlds, I started to think: what if you did a modern-day film sequel? And like that, I imagined an opening sequence: an Air & Space Museum annex, at Dulles (of course — or the rebuilt Dulles, because presumably it had been damaged in the War of the Worlds), filled with planes and spacecraft and other technological achievements of ours, and the camera tracks across the artifacts and the people visiting them until it pans up to show one of these hanging from the ceiling:
An alien vessel, restored but made harmless, though there as a sign — how Independence Day: Resurgence of me to think this way — that maybe the alien invaders would come back. And something you could visualize on a film budget; no way would the TV show have had the money to pull that off. (The show, in fact, portrayed the people of Earth as having "selective amnesia" about the original film's war, with the world rebuilt enough to cover the scars of the war...making the show easier and cheaper to produce, but, again, I digress.)
The Udvar-Hazy Center did appear on film, if you can call Transformers: Revenge of the Fallen a film (hey now!), but more importantly, it appears in reality. One day, I'll be back.