If you look carefully, you can just about make out something that is far more obvious when you're actually walking down it: there are footprints indented into the linoleum.
Here's a magnified view, along with a second version in which I've outlined the footprints more clearly:
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I dimly recall these footprints having been there when I was an undergraduate over 30 years ago. I'm guessing that they're in the concrete floor, and over the years the lino' has conformed to them.
Either that, or someone was carrying boulders down there once.