Betcha don't know what this is.
I didn't. I was confident it was a fancy well cover, but I was wrong. It's not a truncated lookout tower either.
It is early 18th century, on the front of the former priory at Beaulieu-lès-Loches. It is apparently, according to the ever useful Compagnonnage (Artisans Guilds) website, an architectural structure called une trompe ('a trunk'), and a very beautiful one at that.
It seems to have been a sort of outdoor pulpit for the prior, as well as providing internal access to the upper floor of the priory. The technical term in English for its pulpit function is a 'tribune'. In French this architectural feature is often referred to as une trompe de Montpellier, and for those of you who read French there is a nerdy discussion of what the specification for une trompe de Montpellier is and whether this structure fits the description (read the comments). There is also an interesting link to some similar structures known as coquilles ('shells').
It has been 'restored' in the past using cement, which hasn't done it any favours, and it isn't currently in particularly good condition. The soft limestone (tuffeau) has suffered over the years just with the action of the weather upon it.