This is a nice, fresh and enjoyable thread to read.
My longest time outside the country was in Washington DC for several months as a radiology resident doing a radiologic pathology course.
DC always felt a little foreign to me, although it was a little hard to pinpoint the main reason why. It of course was a lot more urban than I was used to, and heavily African American (although the ones I interacted with, including my landlady were uniformly very nice people). My course was at the AFIP (Armed Forces Institute of Pathology), which was on an active military base, and, the US military is a very serious institution. You had to mind your P's and Q's around there. DC just seemed older and more consequential than anything I was used to in Canada, especially hanging around the National Mall and the Smithsonian buildings downtown, as well as all the national memorials. This included the US Capitol and the Supreme Court buildings. There just seemed to be so much gravitas there - certainly more so than in Ottawa (I have spent enough time on Parliament Hill to know the difference), and, in some ways, even London in the UK. I have spent time there too.
In any event, it was a relief to get back to Canada. It just seemed so much more relaxed and laid back. I appreciated the instant familiarity on my return to Halifax (where I lived at the time).