I had, of course, seen Casablanca on Channel 5 in New York when I was a kid.
Channel 5 and Channel 11 showed ALL of the old black and white movies back in the day (Channel 7 showed way-cool 60s movies in their 4:30 Movie) - Cagney, Bogie, the musicals, the Bowery Boys -- Channel 5 gave us everything. So I thought I had seen Casablanca.
Then the Carnegie Hall Cinema showed it one night, so I traveled from Bed-Stuy in Brooklyn to Carnegie Hall to see it - quite alone, of course - I knew no one then (or now) who loved these things like I did. The Carnegie Hall was a nice little upscale revival house -- the first time I had ever seen pastries and lattes in the lobby!
The lights went down, and that map of the world came up on the screen...and I was transported. I honestly don't think that I've come back yet. See this in a theater if the opportunity ever arises.