The case of John Cowan v Hopetoun House Preservation Trust involved a grandfather who had gone on a guided bat-watching walk with his grandson one night at a stately home. After the walk they took the wrong path on their way back to the car park and Mr Cowan decided to walk across the lawn when they fell 5 foot down into a ha-ha.
Now if you don’t watch or read Alan Titchmarsh (a very English thing…) you may not know what a ha-ha is. There is one in the great gardens of Stowe (UK), and he defines it as “a ditch that offered unspoilt views of the surrounding area whilst providing a boundary to farm animals and locals“, and explains that it was so named because visitors would explain “Ha ha” in surprise when coming upon the almost hidden feature.
For the legal viewpoint, see this concise summary published by Brodies LLP.