Another interesting place filled with interesting folk, though you wouldn't be there unless injured, visiting someone injured, or just a wee bit morbid, is the ER. Had the misfortune to visit one last week when I was imagining this post. The common thread, methinks, between an airport and an ER, is that they cater to all-comers and, in general, most of those comers are suffering through some degree of misery, which tends to reduce inhibition and other social filters, allowing for great observation opportunity (hey, if you've got to be there, might as well multi-task, right?).
What about you? Do you have a place you go (or wish you could go - injury free, of course) to people watch?