“Mushigaeshi” (武者返し - literally, repelling assailants) were architectural features designed to, well, repel assailants, ranging from uneven ground stonework to complicated walls. Kumamoto Castle is particularly famous for its mushigaeshi. For example, the stones of the walls are placed at random angles to thwart anyone trying to climb them. They also eventually reach a 90° angle. An interesting example is this location, where the builders figured out they’d screwed up the angle so added another wall. We all have bad days, but most of them don’t involve tons of rock.
Yamaga, famous for its craftsmanship (think of the lanterns they wear on their heads during their festival), recently donated this model of the castle to our city. Note the slopes of the walls. Thanks, Yamaga! - William