I have a real thing for windmills of all types so I love this. And these types make places that can be real great plot points or a focus of an encounter. Now this is an inefficient windmill but my favourites are vertical axis windmills which are even more inefficient =P. Following this type of windmill is one where a small wooden "cap" on the top where shaft protruded would be that could be rotated to face the wind. And following that, they designed it so the entire windmill could rotate.
And there are all kinds of windmill too. Little ones that just operate an archimedes screw to drain fenland and stuff. Others like those ones you see in the US which are simple lattice structures to help irrigate fields. They are so very useful.
Windmills are some of the best things. Huge labour saving devices too! The Romans weren't too big on them because they had slaves but they did the work of dozens and dozens of slaves.
Windmills. Cheer for them!