Cambridge is famous for its university’s and bicycles. Lots and lots of bicycles. With bicycles comes bike locks and this fantastic cache is just off one of the main shopping thoroughfares. I attempted this in the middle of the day, with bikes locked up all around, so I did feel a little conspicuous and quite what I would have said if the bike owner that was locked up next to this had come back at the precise moment, god only knows.
Anyway, sit back and watch this. Clever stuff and like all the best caches, very simple.