C Stock gap at Monument.  Because the station was built on a curve, the track is canted (raised along the outer edge of the curve) to minimise discomfort to passengers.  The cant causes a vertical gap between the train and the platform in addition to the horizontal gap caused by the curve.  The gap is advertised by the "MIND THE GAP" signs on the platform, lights under the platform edge and recorded announcements.  The MD of London Underground was told many years ago that the increase in the number of "Mind the Gap" announcements would become a national joke - and so it has.  You can even buy "Mind the gap" T-shirts now.