with the Orangery in the background
Photo: R. Neil Marshman
I didn't. I was reading about
Kedleston Hall in Derbyshire and the article said the grounds had a ha-ha. A what? So, I clicked on the big W and read all about it. The above pic shows the ha-ha looking towards the house, while the photo below shows the uninterrupted view from the house. It is so-named because of the reaction of most people when happening upon one. One wouldn't be walking at night-time without a torch!
This from Wikipedia: "The Ha-ha is an expression in garden design that refers to a trench, the inner side of which is vertical and faced with stone,, with the outer face sloped and turfed, making the trench, in effect, a sunken fence or retaining wall. The ha-ha is designed not to interrupt the view from a garden, pleasure-ground, or park, and to be invisible until seen from close by."

Castle Ashby - looking over the Ha-ha
Photo: R Neil Marshman
The ha-ha is designed to keep animals from entering the property around a building and can also be used to deter people from getting out; as in the following pics of two lunatic asylums (yep, that's what they were called once) that existed in Melbourne in the 19th and 20th century. The ha-ha enabled the patients to see the outside world.
Melbourne Victoria, c.1900
1848-1925
What would have been a ladies' courtyard
1871-1988
The main building and surrounding grounds of the Kew Asylum (later known as Willsmere) were sold by the government in the 1980s and it is now the site of the exclusive Willsmere Apartments. Many of the ha-ha walls have been repaired and remain intact on the property.
So, there you have it - ha-ha!