One thing the trip has made me think about is airports. Airports are a strange place. In being in one for an hour or two while you transfer, you may be visiting a place you have never been to before. At the same time, you are not really seeing that place, but rather a large hub airport, a sort of culture into itself that exists outside of the local region, and indeed exists more in a series of remote locations. So while individual airports might contain some hints of the civilization just beyond its FAA-run borders - a locally themed gift shop, ads for local businesses, what have you - they all (at least within a given country, and to an extent outside of it) are basically the same place. It's as if one big city were split into a thousand pieces and distributed throughout the US and abroad.
Given that, the list of place I've been doesn't tend to include places where I've only been to the airport. So while I had been to Chicago O'Hare years before now, I hadn't actually been to Chicago until the other day; I had just been to the ORD district of the international airport continuum.
The other parts of the continuum I have visited where I have not visited the surrounding non-airport regions:
BOS (Boston Logan)
MSP (Minneapolis-St. Paul)