Today I looked inside a campus recycling bin on the main quad and saw only a small piece of paper at the bottom.
I quickly realized (because I've seen a lot of different kinds of boarding passes before) that it was a Korean Air boarding pass, and so I picked it up. It wasn't terribly damaged, maybe a tiny bit stained, but the vast majority of the paper was nice and crisp.
The faded thermal printing showed that it was for a flight from Seoul to London, on January 10 of this year.
I wonder how it got there.