I'm always fascinated by fences, walls and the like which seem either inappropriate, ineffective, or inexplicable -- those Mysterious Barricades (relax, I'm not trying to sell you anything today). I collected these two last week.
The first is a double fence on St. Catherine's Hill, near Winchester. There is nothing obvious on the far side of it that is not also on the near side of it. A pure boundary, like a national border, complete with a no-man's-land.
The second is a much repaired but emphatic boundary crossing a stream that runs through the University campus. It doesn't seem to bother the stream much, though it does act as something of a tea-strainer. "Overdetermined" is the word that springs to mind. Or perhaps, "challenge".