I'm a big aerospace history buff. All my vacations seem to involve some sort of museum or historic place to aviation (and I have a very patient wife).
I seem to be doing that a lot lately myself (or rather, with family when I go to visit them). In the past year, I've been to the Wright Brothers' workshop in Greenfield Village in Detroit, the National Air & Space Museum in DC (as my avatar demonstrates), and the Boeing factory tour and Museum of Flight in Seattle.