A: When it has no students.
I spent the second half of last week in Milton Keynes at a meeting hosted by the Open University. I work for a University so I know what the atmosphere is like, especially over the last week or so with students returning for the new academic year.
The Open University isn't like that though because they don't have any students. OK that is not entirely true -- they don't have students at the University, all their students study via distance learning courses. Now this might be great for academics who don't actually like meeting students (I've known a few of those) but it leaves you wondering exactly where you are when you walk around the campus. It is quiet and empty in stark contrast to any other University I have ever visited.
While I may often be heard moaning about there being two many students around I've now decided that too many students is immeasurably preferable to there being no students at all.