maps showing campsites but not warning you that they're only for use by Scouts.
I remember falling foul of this with my buddy Jim on one of my earliest cycle expos, early 90s. We ended up in Wiltshire, somewhere near Salisbury Plain, and headed for the campsite marked on the map. Scouts, and all in residence too. But they let us stay, on condition we pitched at the other end of the field, behind the building, and what's more, in the morning the Arkelas, Brown Owls and Grey Wolves, or whatever they call themselves, made us a cup of tea and some breakfast. All for free!
It wouldn't, as they say, happen now.