Anyhow. I only made it to about 450 characters in the end. It took me half an hour to think of something to write, then 90 minutes to actually write. To match my mood at the time, I settled on "What if I was back home now, and not in Beijing?", and how much nicer it would be to be laying on the beach with friends, instead of writing essays in cold, smoggy Beijing. Then I got to writing about what one learns about one's self, one's country and one's culture when one experiences and studies another. So I eventually managed to write something that sounded half positive.
I really must say I don't enjoy this writing class. I do like seeing the finished product, and I'm sure it's one of the more useful things I could be doing to advance my Chinese... but I think next semester I might choose a spoken Chinese elective instead.